Individually encapsulated solar cells and solar cell strings

ABSTRACT

Methods and devices are provided for improved environmental protection for photovoltaic devices and assemblies. In one embodiment, the device comprises of an individually encapsulated solar cell, wherein the encapsulated solar cell includes at least one protective layer coupled to at least one surface of the solar cell. The protective layer has a chemical composition that prevents moisture from entering the solar cell and wherein light passes through the protective layer to reach an absorber layer in the solar cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.11/462,359 filed Aug. 3, 2006, which claims priority to U.S. ProvisionalApplication Ser. No. 60/746,626 filed May 5, 2006; commonly assigned,copending U.S. Provisional Application Ser. No. 60/746,961 filed May 10,2006; commonly assigned, copending U.S. Provisional Application Ser. No.60/804,570 filed Jun. 12, 2006; commonly assigned, copending U.S.Provisional Application Ser. No. 60/804,571 filed Jun. 12, 2006; andcommonly assigned, copending U.S. Provisional Application Ser. No.60/806,096 filed Jun. 28, 2006. This application is also acontinuation-in-part of copending U.S. patent application Ser. No.11/460,613 filed Jul. 27, 2006. All of the foregoing applications arefully incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

This invention relates generally to solar cells, and more specifically,to protective layers used to protect solar cells, solar cell strings,and/or solar cell modules against environmental exposure damage.

BACKGROUND OF THE INVENTION

Solar cells and solar modules convert sunlight into electricity. Thesedevices are traditionally mounted outdoors on rooftops or in wide-openspaces where they can maximize their exposure to sunlight.Unfortunately, this type of outdoor placement also subjects the solarcells and solar cell modules to substantially constant weather andmoisture exposure. Due to this constant and extended exposure to theelements, solar cells and solar cell modules are preferably designed tohave sufficient environmental protection to provide many years of stableand reliable operation without failure due to moisture damage or otherexposure related damage. Even small solar cells for use with consumerelectronic devices should have rugged environmental protection as thesedevices are by their nature also generally used outdoors or in areas ofsun exposure where they can maximize their electric generating ability.

A central challenge in finding suitable encapsulating material for usewith solar cells is finding one material that has best-in-classqualities for the many properties desired in a good environmentalencapsulant. There may be some materials that provide good moisturebarrier qualities but are not sufficiently transparent to pass lightdown to the absorber layer in the solar cell. Other layers may be goodat moisture and transparent, but discolor over time and reducestransparency with ongoing use.

Traditional solar cell modules address the weatherproofing issue byusing a glass sheet of sufficient size to cover all the cells in a solarmodule. Although glass provides a very durable and weather resistantlayer, it does so at the cost of being expensive, heavy, and rigid.Glass modules are also generally more challenging to manufacture in ahigh-throughput manner. The use of glass also typically involves usingsome type of edge tape to prevent moisture from entering laterally. Thisfurther complicates the manufacturing process as it is difficult toavoid gaps in the barrier, especially at the interfaces of the edge tapeand the glass as well as the edge tape and any bottom layer.

Furthermore, thin-film solar cells are more sensitive to moistureexposure than traditional silicon based solar cells. It is generallyundesirable to expose any type of solar cell to direct moisture contact.This is even more true for thin-film solar cells. Hence, it is importantthat weatherproofing and moisture protection for thin-film solar cellsequal or exceed those levels provided to silicon based cells.

Due to the aforementioned issues, improved environmental protectionconfigurations are desired for solar cells, solar cell modules, and/orsimilar photovoltaic devices.

SUMMARY OF THE INVENTION

Embodiments of the present invention address at least some of thedrawbacks set forth above. The present invention provides for theimproved environmental protection of solar cells generally and thin-filmsolar cells in particular. It should be understood that this inventionis generally applicable to any type of solar cell, whether they arerigid or flexible in nature or the type of material used in the absorberlayer. Embodiments of the present invention may be adapted forroll-to-roll and/or batch manufacturing processes. At least some ofthese and other objectives described herein will be met by variousembodiments of the present invention.

The present invention provides methods and devices for improvedenvironmental protection for photovoltaic devices and assemblies. In oneembodiment, the device comprises of an individually encapsulated solarcell, wherein the encapsulated solar cell includes at least oneprotective layer coupled to at least one surface of the solar cell. Theprotective layer has a chemical composition that prevents moisture fromentering the solar cell and wherein light passes through the protectivelayer to reach an absorber layer in the solar cell. It should beunderstood that the protective layer described herein can be applied toany type of photovoltaic device and is not limited to thin-film,organic, or silicon based solar cells. Individual encapsulation of thecell and/or cell string can effectively address the issue of lateralingress of vapor between the top and bottom protective sheets.

In one embodiment of the present invention, a device is providedcomprised of an individually encapsulated solar cell, wherein theencapsulated solar cell includes at least one protective layer coupledto at least one surface of the solar cell. The protective layer has achemical composition that substantially prevents moisture from enteringthe solar cell, wherein light passes through the protective layer toreach an absorber layer in the solar cell.

For any of the embodiments described herein, the following may alsoapply. In one embodiment, the protective layer may be comprised of asubstantially organic material. In another embodiment, the protectivelayer may be comprised of a heat curable hardcoat material. Theprotective layer may be a radiation curable hardcoat material. Theprotective layer may be a UV curable hardcoat material. The protectivelayer may be a clear, non-yellowing silicone-based hardcoat material.The protective layer may be a curable polyacrylate hardcoat containingsilica particles.

For any of the embodiments described herein, the following may alsoapply. The protective layer may include an acrylic compositioncontaining at least one filler material, at least one multifunctionalacrylic material, and at least one higher functional acrylic material.The filler material may be silica, functionalized silica, and/oracrylate functionalized silica. The filler material may be in the formof nanoparticles having maximum dimensions of about 1 micron or less.The filler material may be a silicone based material. The fillermaterial may include a colloidal silica and a silane selected from thegroup consisting of: 3-methacryloxypropyltrimethoxysilane,3-acryloxypropyltrimethoxysilane, 2-methacryloxyethyltrimethoxysilane,2-acryloxyethyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane,3-acryloxypropyltriethoxysilane, 2-methacryloxyethyltriethoxysilane,2-acryloxyethyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane,2-glycidoxyethyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane,2-glycidoxyethyltriethoxysilane, and/or combinations thereof.

For any of the embodiments described herein, the multifunctional acrylicmaterial may be selected from the group of: diacrylates, such as1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, ethylene glycoldiacrylate, diethylene glycol diacrylate, tetraethylene glycoldiacrylate, tripropylene glycol diacrylate, neopentyl glycol diacrylate,1,4-butanediol dimethacrylate, poly(butanediol) diacrylate,tetraethylene glycol dimethacrylate, 1,3-butylene glycol diacrylate,triethylene glycol diacrylate, triisopropylene glycol diacrylate,polyethylene glycol diacrylate, and bisphenol; dimethacrylate;triacrylates such as trimethylolpropane triacrylate, trimethylolpropanetrimethacrylate, pentaerythritol monohydroxy triacrylate, andtrimethylolpropane triethoxy triacrylate; tetraacrylates, such aspentaerythritol tetraacrylate and di-trimethylolpropane tetraacrylate;and pentaacrylates, such as dipentaerythritol; (monohydroxy)pentaacrylate, or combinations thereof.

For any of the embodiments described herein, the following may alsoapply. The higher multifunctional acrylic material is selected from thegroup consisting of: triacrylates such as trimethylolpropanetriacrylate, trimethylolpropane trimethacrylate, pentaerythritolmonohydroxy triacrylate, and trimethylolpropane triethoxy triacrylate;tetraacrylates, such as pentaerythritol tetraacrylate anddi-trimethylolpropane tetraacrylate; and pentaacrylates, such asdipentaerythritol; and/or (monohydroxy) pentaacrylate. Combinations ofany of the foregoing is also envisioned. It should be understood that aninitiator and/or a photoinitiator may be combined in the hardcoat. Thephotoinitiator may be selected from the group consisting of:2-hydroxy-2-methyl-1-phenyl-propan-1-one or2,2-dimethoxy-2-phenyl-acetyl-phenone, and/or combinations thereof. Theuncured hardcoat may also include an anaerobic gelation inhibitor. Theanaerobic gelation inhibitor may be selected from the group consistingof: 2,2,6,6-tetramethylpiperidinyloxy,4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy,bis(4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy sebacate diradical,2,2-diphenyl-1-picrylhydrazyl, 1,3,5-triphenylverdazyl,1-nitroso-2-naphthol, a nitrone, methylhydroquinone, galvinoxyl,4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy, N-t-butyl-α-phenyl nitrone,2,2-diphenyl-1-picryl-hydrazyl hydrate (DPPH), and/or combinationsthereof. The hardcoat precursor may also include a diluent. The diluentmay be selected from the group consisting of: isopropanol, t-butanol,n-propanol, n-butanol, methanol, ethanol, ethylene glycol n-butyl ether,and mixtures thereof.

For any of the embodiments described herein, the following may alsoapply. In one embodiment, the protective layer may have a compositioncomprised of 2 at. % silicon, 32 at. % carbon, 17 at. % oxygen, and 48at. % hydrogen. In another embodiment, the protective layer has acomposition comprised of 1-4 at % silicon, 20-40 at % carbon, 40-60%hydrogen, and 10-30% oxygen. Optionally, the protective layer has acomposition comprised of 1-4 at % silicon, 20-40 at % carbon, 10-30%oxygen, and the balance made up of hydrogen. The protective layer may becomprised of a substantially inorganic material. The protective layermay be comprised of at least one material selected from the groupconsisting of: silica, alumina, aluminosilicates, diamond-like films,borosilicates, silicon nitride, aluminophosphosilicates,aluminophosphates, and/or combinations thereof. The protective layer mayinclude a first layer of a first inorganic material and a second layerof a second inorganic material. The protective layer may include a layerof silica and a layer of alumina. The protective layer may include aplurality of fused inorganic particles. The protective layer may includea plurality of fused silica particles. The protective layer may be alayer deposited by atomic layer deposition. The protective layer may becomprised of a plurality of layers deposited by atomic layer deposition.The protective layer may be a silico-acrylic composition.

For any of the embodiments described herein, the following may alsoapply. Although not limited to the following, the protective layer mayhave a thickness in the range of about 1 to about 1000 nm. In anotherembodiment, the protective layer may have a thickness in the range ofabout 1 to about 500 nm. In another embodiment, the protective layer mayhave a thickness in the range of about 0.3 to about 300 nm. In anotherembodiment, the protective layer may have a thickness in the range ofabout 50 to about 200 nm. In some embodiments, the protective layer maybe thicker, in the range of about 1 to about 500 microns. In otherembodiments, may be in the range of about 50 to about 150 microns. Theprotective layer may include an organic material and an inorganicmaterial. The protective layer may be a hybrid nanolaminate having aplurality of layers. The protective layer may include a plurality oflayers of an inorganic material; and a plurality of layers of an organicmaterial wherein the layers of organic material alternate with thelayers of inorganic material. The adjacent layers of the organicmaterial and the inorganic material may be covalently bonded layerscharacterized by covalent bonds that couple adjacent layers together.The total number of layers of organic polymer and layers of inorganicmaterial in the film may be between about 100 and about 1000 layers, orbetween about 1000 and about 10,000 layers, or between about 10,000layers and about 100,000 layers. Each of the layers of inorganicmaterial may have a thickness of about 0.1 nm to about 1 nm; about 1 toabout 10 nm; or about 1 nm to about 100 nm. The protective layer may bea templated nanolaminate layer with nanoparticle beads.

For any of the embodiments described herein, the following may alsoapply. The solar cell may be a non-silicon based solar cell. The solarcell may be an amorphous solar cell. The solar cell may be acopper-indium-selenide based alloy. The solar cell may include anabsorber layer having one or more inorganic materials from the groupconsisting of: titania (TiO2), nanocrystalline TiO2, zinc oxide (ZnO),copper oxide (CuO or Cu2O or CuxOy), zirconium oxide, lanthanum oxide,niobium oxide, tin oxide, indium oxide, indium tin oxide (ITO), vanadiumoxide, molybdenum oxide, tungsten oxide, strontium oxide,calcium/titanium oxide and other oxides, sodium titanate, potassiumniobate, cadmium selenide (CdSe), cadmium suflide (CdS), copper sulfide(Cu2S), cadmium telluride (CdTe), cadmium-tellurium selenide (CdTeSe),copper-indium selenide (CuInSe2), cadmium oxide (CdOx), CuI, CuSCN, asemiconductive material, or combinations of the above. The solar cellmay include an absorber layer having one or more organic materials fromthe group consisting of: a conjugated polymer, poly(phenylene) andderivatives thereof, poly(phenylene vinylene) and derivatives thereof(e.g., poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene(MEH-PPV), poly(para-phenylene vinylene), (PPV)), PPV copolymers,poly(thiophene) and derivatives thereof (e.g.,poly(3-octylthiophene-2,5,-diyl), regioregular,poly(3-octylthiophene-2,5,-diyl), regiorandom,Poly(3-hexylthiophene-2,5-diyl), regioregular,poly(3-hexylthiophene-2,5-diyl), regiorandom), poly(thienylenevinylene)and derivatives thereof, and poly(isothianaphthene) and derivativesthereof,2,2′7,7′tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene(spiro-MeOTAD), organometallic polymers, polymers containing perylene units,poly(squaraines) and their derivatives, and discotic liquid crystals,organic pigments or dyes, a Ruthenium-based dye, a liquidiodide/triiodide electrolyte, azo-dyes having azo chromofores (—N═N—)linking aromatic groups, phthalocyanines including metal-freephthalocyanine; (HPc), perylenes, perylene derivatives, Copperpthalocyanines (CuPc), Zinc Pthalocyanines (ZnPc), naphthalocyanines,squaraines, merocyanines and their respective derivatives,poly(silanes), poly(germinates),2,9-Di(pent-3-yl)-anthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10-tetrone,and2,9-Bis-(1-hexyl-hept-1-yl)-anthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10-tetroneand pentacene, pentacene derivatives and/or pentacene precursors, anN-type ladder polymer, poly(benzimidazobenzophenanthroline ladder)(BBL), or combinations of the above. The solar cell may include anabsorber layer having one or more materials from the group consistingof: an oligimeric material, micro-crystalline silicon, inorganicnanorods dispersed in an organic matrix, inorganic tetrapods dispersedin an organic matrix, quantum dot materials, ionic conducting polymergels, sol-gel nanocomposites containing an ionic liquid, ionicconductors, low molecular weight organic hole conductors, C60 and/orother small molecules, or combinations of the above. The solar cell mayinclude an absorber layer having one or more materials from the groupconsisting of: a nanostructured layer having an inorganic poroustemplate with pores filled by an organic material (doped or undoped), apolymer/blend cell architecture, a micro-crystalline silicon cellarchitecture, or combinations of the above.

For any of the embodiments described herein, the following may alsoapply. The solar cell may be a rigid solar cell. The solar cell may be aflexible solar cell. The protective layer may fully encapsulate thesolar cell. The protective layer may cover a top surface and all sidesurfaces of the solar cell. The protective layer may cover a topsurface, a bottom surface, and all side surfaces of the solar cell. Theprotective layer may be a transparent colorless layer. The protectivelayer may be a solution deposited protective layer. The protective layermay be an ALD deposited protective layer. The protective layer may beapplied to each solar cell prior to mounting the solar cell in aphotovoltaic device module.

For any of the embodiments described herein, the following may alsoapply. The unprotected solar cell may have a lower conversion efficiencythan the solar cell with the protective layer. The protective layer mayhave a water vapor transmission rate (WVTR) sufficiently low so thatthere is substantially no loss in solar cell conversion efficiency whenthe cell is exposed for 1000 hours at 85° C. and 85% relative humidity.The protective layer may have a WVTR such that the conversion efficiencyof a cell with the protective layer has a conversion efficiency at least25% better than an unprotected cell after both are exposed for 1000hours at 85° C. and 85% relative humidity. The protective layer may havea WVTR such that the conversion efficiency of a cell with the protectivelayer has a conversion efficiency at least 50% better than anunprotected cell after both are exposed for 1000 hours at 85° C. and 85%relative humidity.

In another embodiment of the present invention, a cell string may becomprised of an encapsulated cell string, wherein the string comprisesof a plurality of solar cells coupled together. The encapsulated cellstring includes at least one protective layer covering the plurality ofsolar cells, the protective layer having a chemical composition thatprevents moisture from entering each of the solar cells, wherein lightpasses through the protective layer to reach an absorber layer in eachof the solar cells.

In yet another embodiment of the present invention, a photovoltaicdevice module comprising a support substrate and a plurality ofindividually encapsulated solar cells mounted on the support substrate.Each of the solar cells may have a protective layer, wherein theprotective layer provides weatherproofing to the solar cells therein.The protective layer may also be above the solar cell and light passesthrough the protective layer to reach the solar cell.

In a still further embodiment of the present invention, a photovoltaicdevice module comprising a plurality of solar cells sandwiched betweenat least one top layer and at least one bottom layer. Each of the cellsmay have a protective layer that provides a higher level of moistureresistance than any of the layers above the cell, wherein the protectivelayer is above the solar cell and light passes through the protectivelayer to reach the solar cell.

In another embodiment of the present invention, a method comprises ofproviding a solar cell having an absorber layer and forming a protectivelayer to the solar cell using a solution-deposition process. Theprotective layer provides a moisture barrier that substantially preventsmoisture damage to the absorber layer.

For any of the embodiments described herein, the following may alsoapply. The forming step may be comprised of using a substantiallyorganic material. The forming step may be comprised of using a heatcurable hardcoat material. The forming step may be comprised of using aradiation curable hardcoat material. The forming step may be comprisedof using a UV curable hardcoat material. The forming step may becomprised of using a clear, non-yellowing silicone-based hardcoatmaterial. The forming step may be comprised of using a curablepolyacrylate hardcoat containing silica particles. The forming stepcomprises using a composition containing at least one filler material,at least one multifunctional acrylic material, and at least one higherfunctional acrylic material. The filler material, the multifunctionalacrylic material, the higher multifunctional acrylic material, aninitiator, a photoinitiator, an anaerobic gelation inhibitor, and/or adiluent may be any of the material mentioned previously herein.

For any of the embodiments described herein, the following may alsoapply. The forming step may be comprised of using a substantiallyinorganic material. Optionally, the forming step comprises of using atleast one material selected from the group consisting of: silica,alumina, aluminosilicates, diamond-like films, borosilicates, siliconnitride, aluminophosphosilicates, aluminophosphates, and/or combinationsthereof. The protective layer may be comprised of a first layer of afirst inorganic material and a second layer of a second inorganicmaterial. The protective layer may be comprised of a layer of silicalayer and a layer of alumina. The protective layer may be comprised of aplurality of fused inorganic particles. The protective layer may becomprised of a plurality of fused silica particles. The protective layermay be comprised of a layer deposited by atomic layer deposition. Theprotective layer may be comprised of a plurality of layers deposited byatomic layer deposition. The protective layer may be comprised of asilico-acrylic composition. The protective layer may have a thickness inthe range of about 0.3 to 300 nm. The protective layer may be comprisedof an organic material and an inorganic material. The protective layermay be comprised of a hybrid nanolaminate having a plurality of layers.The forming step may be comprised of forming hybrid organic/inorganicnanolaminate. The forming step may be comprised forming a barrierwaveguide film. The forming step may be comprised of using aroll-to-roll manufacturing process. Forming the protective layer mayinvolve using a batch process. Forming the protective layer involvessolution depositing a material to be processed into the protective layeron the solar cell.

For any of the embodiments described herein, the following may alsoapply. Forming the protective layer may be comprised of using at leastone method from the group consisting of: wet coating, spray coating,spin coating, doctor blade coating, contact printing, top feed reverseprinting, bottom feed reverse printing, nozzle feed reverse printing,gravure printing, microgravure printing, reverse microgravure printing,comma direct printing, roller coating, slot die coating, meyerbarcoating, lip direct coating, dual lip direct coating, capillary coating,ink jet printing, jet deposition, spray deposition, aerosol spraydeposition, dip coating, web coating, microgravure web coating, orcombinations thereof. The protective layer may be comprised of asilico-acrylic composition containing silica, a solvent and at least onemultifunctional acrylic monomer. Forming step may be comprised offorming a plurality of protective sublayers. The forming step may becomprised of forming a first layer, curing the first layer, and thenapplying a second layer over the first layer. The protective layer maybe applied to each solar cell prior to mounting the solar cell in aphotovoltaic device module. The present invention also envisions amoisture resistant solar cell formed by the method as set forth herein.

In yet another embodiment of the present invention, a method comprisesof providing at least one cell string having a plurality of solar cellseach having an absorber layer. The method may include forming aprotective layer cover the cell string and each of the solar cells,wherein the protective layer provides a moisture barrier that preventsmoisture damage to the absorber layer.

In yet another embodiment of the present invention, a method comprisesof providing a plurality of solar cells each having an absorber layer.The method may include forming a protective layer covering at least oneof the solar cells and placing the cells on a module support. Theprotective layer may provide a moisture barrier that prevents moisturedamage to the absorber layer.

In another embodiment of the present invention, solar cells may beprotected from the environment, particularly water, by an ultrathin filmof transparent inorganic material (dielectric), which may be formed fromsilica-containing precursors or from atomic layer deposition ofdielectric precursors, with or without the presence of small (nanoscale)silica or other dielectric particles, or by sintering such particlesusing rapid thermal processes which do not heat the underlyingsubstrate. The ability to make good barriers at low cost, and especiallydirectly on top of the cell, thereby protecting both the top and edges,and may be desirable to enable a wider choice of materials for theprotective layers. In one embodiment, the method may involve the use ofsilica particles to provide most of the barrier, coupled with “fillers”provided from fluid phases (either liquid or gas) to connect them.Alternatively the method may involve heating the particles with RTP tofuse them while still not damaging the substrate. In yet anotherembodiment, atomic layer deposition may be used to place a barrierdirectly on the cell.

A further understanding of the nature and advantages of the inventionwill become apparent by reference to the remaining portions of thespecification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C show cross-sectional views of a solar cell with a protectivelayer according to various embodiments of the present invention.

FIG. 2 shows a solar cell with a substantially organic protective layeraccording to one embodiment of the present invention.

FIG. 3 is a schematic showing various components in an organic-basedprotective layer according to embodiments of the present invention.

FIG. 4 shows a solar cell with a substantially inorganic protectivelayer according to one embodiment of the present invention.

FIGS. 5A and 5B show the fusing of inorganic particles to form aprotective layer according to one embodiment of the present invention.

FIG. 6 shows a solar cell with a hybrid organic/inorganic protectivelayer according to one embodiment of the present invention.

FIG. 7 shows a close-up cross-sectional view of the hybridorganic/inorganic protective layer according to one embodiment of thepresent invention.

FIG. 8 shows one embodiment of a templated hybrid organic/inorganicprotective layer according to one embodiment of the present invention.

FIG. 9 shows a close-up view of the templated hybrid organic/inorganicprotective layer according to one embodiment of the present invention.

FIG. 10 is a schematic showing one method of forming the protectivelayer according to various embodiments of the present invention.

FIG. 11 shows one embodiment of a method for curing a protective layeraccording to the present invention.

FIG. 12 shows one embodiment of a method for coating a cell string witha protective layer according to the present invention.

FIG. 13 is a cross-sectional view showing a module with individuallyencapsulated solar cells according to one embodiment of the presentinvention.

FIG. 14 is a cross-sectional view showing a module with multi-ply layersaround individually encapsulated solar cells according to one embodimentof the present invention.

FIG. 15 shows a technique for handling rigid substrate according to oneembodiment of the present invention.

FIG. 16 shows a roll-to-roll technique for applying a protective layeraccording to one embodiment of the present invention.

FIG. 17 shows another roll-to-roll technique for applying a protectivelayer according to one embodiment of the present invention.

FIG. 18 shows a flexible solar assembly having solar cells with theprotective layer according to one embodiment of the present invention.

FIG. 19 shows a photovoltaic roofing material having solar cells withthe protective layer according to one embodiment of the presentinvention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed. It may be notedthat, as used in the specification and the appended claims, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise. Thus, for example, reference to “a material”may include mixtures of materials, reference to “a compound” may includemultiple compounds, and the like. References cited herein are herebyincorporated by reference in their entirety, except to the extent thatthey conflict with teachings explicitly set forth in this specification.

In this specification and in the claims which follow, reference will bemade to a number of terms which shall be defined to have the followingmeanings:

“Optional” or “optionally” means that the subsequently describedcircumstance may or may not occur, so that the description includesinstances where the circumstance occurs and instances where it does not.For example, if a device optionally contains a feature for aanti-reflective film, this means that the anti-reflective film featuremay or may not be present, and, thus, the description includes bothstructures wherein a device possesses the anti-reflective film featureand structures wherein the anti-reflective film feature is not present.

Individually Encapsulated Solar Cells

Referring now to FIG. 1A, one embodiment of the present invention willnow be described. This embodiment shows a configuration of the presentinvention that provides improved environmental protection for a solarcell 10. Individual encapsulation of the solar cell and/or cell stringeffectively addresses a variety of environmental protection issues suchas, but not limited to, lateral ingress of vapor between the top andbottom protective sheets of a solar module. It may also allow forfabrication of new types of solar assemblies where module level barrierrequirements and/or materials used for those barriers are relaxed sincethe cells and/or cell strings may be individually protected.

FIG. 1A shows an exploded view where the various layers are spaced apartfor ease of illustration. The solar cell 10 is shown to be encapsulatedby a protective layer 20. The protective layer 20 fully encapsulates allsides of the solar cell 10 as shown in FIG. 1A. Optionally, it should beunderstood that some embodiments of the present invention may involve aprotective layer 20 that covers less than all sides of the solar cell10. Preferably, the protective layer 20 covers at least one surface ofthe solar cell 10 to provide the desired environmental protection. Inone embodiment, the protective layer 20 covers at least a top surface ofthe solar cell 10 that receives sunlight. In another embodiment, theprotective layer 20 covers the top surface and a plurality of sidesurfaces of the solar cell 10 to provide the desired environmentalbarrier.

In the embodiment of FIG. 1A, the solar cell 10 with protective layer 20may be mounted in a solar cell packaging that includes one or morepottant layers 30 and 32. The packaging may be sized to include onesolar cell 10 or more than one solar cell 10. Optionally, the pottantlayers 30 and 32 may be made of a material such as, but not limited to,a thermoplastic polyurethane, a thermosetting ethylene vinyl acetate(EVA), a thermoplastic such as polyvinyl butyral (PVB), a thermoplasticfluoropolymer such as a copolymer of tetrafluoroethylene,hexafluoropropylene and vinylidene fluoride (THV), a silicone basedmaterial, and/or a thermoplastic ionomer resin such as but not limitedto DuPont Surlyn®. Although not limited to the following, the thicknessof pottant layer 30 may be between 10 microns and 1000 microns, between10 microns and 500 microns in another embodiment, and/or between 100 and300 microns in a still further embodiment. Layer 32 may be of similar ordifferent thickness.

The packaging shown in the embodiment of FIG. 1A may include at leastone outer barrier layer 40. The outer barrier layer 40 may be a temperedglass superstrate that provides structural support and environmentalprotection. In other embodiments, the outer barrier layer 40 may becomprised of more flexible materials that are easier to handle andassemble in a high-throughput manner. As a nonlimiting example, thelayer 40 may be comprised of a co-polymer of ethylene andtetrafluoroethylene (ETFE), or UV cured, highly cross-linked acrylichardcoat rated at 2H, 3H, or 4H pencil scratch resistance, rated at lessthan 10% haze after 500 cycles of 500 g load, CS10F wheels, TaberAbrader. The ETFE may be a modified ETFE (ethylene-tetrafluoroethylene)fluoropolymer such as Tefzel®. Tefzel® combines superior mechanicaltoughness with chemical inertness that approaches that of Teflon®fluoropolymer resins. Tefzel® features a specific gravity of about 1.7and high-energy radiation resistance. Most grades are rated forcontinuous exposure at 150° C. (302° F.), based on a 20,000-hrcriterion.

The packaging shown in the embodiment of FIG. 1A may include at leastone backside support layer 50. The backside support layer 50 maybecomprised of a variety of materials. In one nonlimiting example, layer50 may be selected from the following example of back sheets:Tedlar®-polyester-Tedlar® (TPT), Tedlar®-polyester (TP),Tedlar®-aluminum-polyester (TAP), Tedlar®-aluminum-polyester-Tedlar®(TAPT), and/or Tedlar®-aluminum-polyester-EVA (TAPE). Tedlar® comprisesof polyvinyl fluoride (PVF) and is available from Dupont. Theseconventional back sheets also contain adhesive tie layers andadhesion-promoting surface treatments that are proprietary to the backsheet vendors. Conventional back sheets are available from Isovolta ofAustria and Madico of USA. Layer 50 may optionally be selected from thefollowing examples of unconventional back sheets: aluminum sheet;galvanized steel; Galvalume® 55% aluminum-zinc alloy coated sheet steel;conversion-coated steel such as chromate-based, phosphate-based, orsimilar corrosion-resistant coated sheet steel; plasticized orunplasticized polyvinylchloride (PVC) formulations; aliphatic ether oraliphatic ester or aromatic ether or aromatic ester thermoplasticpolyurethanes; ethylene-propylene-diene (EPDM) rubber sheet;thermoplastic polyolefin (TPO) sheet, polypropylene sheet, polyethylenesheet, polycarbonate sheet, acrylic sheet, and/or single or multiplecombinations thereof.

It should be understood that edge sealing material 54 (shown in phantom)may optionally be used to prevent moisture penetration along the sidesof the various layers 30, 32, 40, and 50. The edge sealing material 54may be selected from the group consisting of: butyl rubber tape, butylrubber tape with desiccant powder, epoxy, flexiblized epoxy, epoxy withdesiccant, flexiblized epoxy with desiccant, or combinations thereof.

Referring now to FIG. 1B, a solar cell 10 is shown with electrical leads22. The electrical leads 22 may extend outward from the individuallyencapsulated solar cell 10 to connect to another cell, to a cell string,or to another solar cell module. The leads 22 may be placed beforeand/or during and/or after the formation of the protective layer 20.Optionally, the leads 22 may be added after the protective layer 20 isformed. In still other embodiments, the leads 22 may also be coated witha material similar to that used for the protective layer 20. FIG. 1Balso shows that a layer 25 of material may such as but not limited tosilica and/or alumina may be coated on one side of the layer 40. Itshould be understood that in some embodiments, the backside support 50may be comprised of a roofing membrane or some other housingconstruction material. This may facilitate integration of photovoltaiccapability with such materials.

Referring now to FIG. 1C, it should be understood that optionally theindividually encapsulated solar cell 10, pottant layers 30 and 32, outerbarrier layer 40 and backside support 50 may be covered with aprotective barrier 60 (shown in phantom). The material used for theprotective barrier 60 may be similar to that used for the protectivelayer 20. This protective barrier 60 may be coated after the layers andcells are coupled together. Other embodiments may be configured so thatat least some or all of the layers and components are coated withbarrier 60 prior to full assembly.

Substantially Organic Protective Layer

Referring now to FIG. 2, it should be understood that a variety ofmaterials may be adapted for use as the protective layer 20. In oneembodiment of the present invention, a substantially organic materialmay be adaptable for use as the protective layer 20. Specifically,organically-based hardcoat materials may be suitable for use with asolar cell 10. As seen in FIG. 2 showing protective layer 20 and layer21 (shown in phantom), more than one layer of the hardcoat may beapplied to address any defects that may be found if only one layer ofthe hardcoat is applied. Hardcoats that may be suitable include acrylichardcoats, acrylic silicone hardcoats, silicone hardcoats, silicahardcoats, or the like. These hardcoats may be hardcoats that are curedby ultraviolet techniques, electron-beam irradiation techniques, otherradiation techniques, thermal heating techniques, or other curingtechniques. Alternatively, hardcoats may also be in the form ofpre-formed layers that are adhered to the target surface by othertechniques.

Referring now to FIG. 3, one embodiment of the present invention may usea curable, substantially organic hardcoat protective layer coupled tothe solar cell 10. By way of nonlimiting example, the composition ofsuitable hardcoat protective layers will be described herein. Thecurable hardcoat protective layer may be comprised of an acryliccomposition containing multiple Components A, B, and/or C. As seen inFIG. 3, the acyrlic composition may optionally include other componentssuch as but not limited to Components D and/or E in addition to theComponents A, B, and/or C.

Component (A) of such an acrylic composition may be comprised of amultifunctional (meth)acrylate oligomer and/or a multifunctional(meth)acrylate monomer. Although not limited to the following, theseoligomers and/or monomers are preferably photopolymerizable materials.In one embodiment, Component (A) may include at least one acrylate ormethacrylate monomer which contains two or more acrylate or methacrylatefunctional groups. Some preferred multifunctional acrylate monomersuseable as Component (A) include: diacrylates, such as 1,6-hexanedioldiacrylate, 1,4-butanediol diacrylate, ethylene glycol diacrylate,diethylene glycol diacrylate, tetraethylene glycol diacrylate,tripropylene glycol diacrylate, neopentyl glycol diacrylate,1,4-butanediol dimethacrylate, poly(butanediol) diacrylate,tetraethylene glycol dimethacrylate, 1,3-butylene glycol diacrylate,triethylene glycol diacrylate, triisopropylene glycol diacrylate,polyethylene glycol diacrylate, and bisphenol A dimethacrylate;triacrylates such as trimethylolpropane triacrylate, trimethylolpropanetrimethacrylate, pentaerythritol monohydroxy triacrylate, andtrimethylolpropane triethoxy triacrylate; tetraacrylates, such aspentaerythritol tetraacrylate and di-trimethylolpropane tetraacrylate;and pentaacrylates, such as dipentaerythritol; or (monohydroxy)pentaacrylate. These multifunctional acrylate monomers are commerciallyavailable from Aldrich Chemical Company, Inc., Milwaukee, Wis.

The second Component (B) may include silica for example in the form of acolloidal dispersion. Useful in the present invention are dispersions ofsilica (SiO₂) particles suspended in water and/or in an organic solventmixture. The dispersion of colloidal silica comprises 1 percent to 70percent, optionally 55 percent to 70 percent, of the coatingcomposition. Colloidal silica is available in both acidic and basicform. Either form may be utilized. Examples of useful colloidal silicainclude: Nalco 1034A colloidal silica, Nalco 1129 colloidal silica,Nalco 2327 colloidal silica, Nalco 2326 colloidal silica and Nalco 1140colloidal silica, which can be obtained from Nalco Chemical Company,Naperville, Ill.

It should be understood that the silica or other filler particles may bepresent in Component (B) as nanoscale particles. The particles may be ofspherical, planar, oblong, flake, other shapes, or combinations of theforegoing shapes. When measured along their longest dimension, they maybe at a size less than about 1 micron. Optionally, they may be less thanabout 500 nm. In other embodiments, they may be less than 250 nm. Instill other embodiments, the silica particles may be less than about 100nm. The silica particles may have an average particle diameter of about5 to about 1000 nm, between about 10 to about 50 nm in anotherembodiment. Average particle size can be measured using transmissionelectron microscopy to count the number of particles of a givendiameter.

Optionally, the second Component (B) may be comprised of a siloxanematerial, with or without silica particles. In one embodiment, theComponent (B) may be an organopolysiloxane comprising a silyl acrylateand aqueous colloidal silica. The silyl acrylate may bev-methacryloxypropyltrimethoxysilane. This provides a rapidly UV curableorganopolysiloxane hardcoat composition. Optionally, the Component (B)may be acryloxy or glycidoxy functional silanes or mixtures thereof.Specific examples of acryloxy-functional silanes include:3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane,2-methacryloxyethyltrimethoxysilane, 2-acryloxyethyltrimethoxysilane,3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltriethoxysilane,2-methacryloxyethyltriethoxysilane, and/or2-acryloxyethyltriethoxysilane. Specific examples of usefulglycidoxy-functional silanes include the following:3-glycidoxypropyltrimethoxysilane, 2-glycidoxyethyltrimethoxysilane,3-glycidoxypropyltriethoxysilane, and/or2-glycidoxyethyltriethoxysilane. The foregoing materials may be used tofunctionalize the silica particles. The functionalized particles maybond intimately and isotropically with an organic matrix defined by theother components. Although not limited to the following, the silicaparticles are typically functionalized by adding a silylacrylate toaqueous colloidal silica.

The third Component (C) may be a material useful for initiating and/orfacilitating curing of the composition. For example, the acryliccomposition may be crosslinked by a variety of methods such as but notlimited to ultraviolet light, heat, or electron beam radiation exposure.If ultraviolet light is used to crosslink the coating composition,inclusion of a photoinitiator into the coating composition is desired.The photoinitiator, when one is employed, may comprise up to 10 percentof the composition, 0.5 to 3 percent in another embodiment. There are nospecial restrictions on the photoinitiators as long as they can generateradicals by the absorption of optical energy. By way of nonlimitingexample, suitable photoinitiators include2-hydroxy-2-methyl-1-phenyl-propan-1-one (Darocur®1173), sold by EMIndustries, Inc., Hawthorne, N.Y., and2,2-dimethoxy-2-phenyl-acetyl-phenone (Irgacure®651), sold by Ciba-GeigyCorporation, Hawthorne, N.Y. In addition, oxygen inhibitors may also beused in conjunction with the photoinitiators. A preferred oxygeninhibitor is 2-ethylhexyl-para-dimethylaminobenzoate, available asUvatone®8303, from The Upjohn Company, North Haven, Conn. Of course,compositions using other techniques for curing may include other typesof initiators.

A fourth Component (D) may optionally be included in some embodiments ofthe present composition. Component (D) may be selected from thematerials listed for Components A, B, or C. As a nonlimiting example,the Component D may be another multifunctional (meth)acrylate oligomerand/or a multifunctional (meth)acrylate monomer selected from the grouppresented for Component A. In such an embodiment, both a diacrylate anda higher functional acrylate are used. Such an embodiment of thecomposition may include at least two materials selected from the listcomprised of: diacrylates, such as 1,6-hexanediol diacrylate,1,4-butanediol diacrylate, ethylene glycol diacrylate, diethylene glycoldiacrylate, tetraethylene glycol diacrylate, tripropylene glycoldiacrylate, neopentyl glycol diacrylate, 1,4-butanediol dimethacrylate,poly(butanediol) diacrylate, tetraethylene glycol dimethacrylate,1,3-butylene glycol diacrylate, triethylene glycol diacrylate,triisopropylene glycol diacrylate, polyethylene glycol diacrylate, andbisphenol; dimethacrylate; triacrylates such as trimethylolpropanetriacrylate, trimethylolpropane trimethacrylate, pentaerythritolmonohydroxy triacrylate, and trimethylolpropane triethoxy triacrylate;tetraacrylates, such as pentaerythritol tetraacrylate anddi-trimethylolpropane tetraacrylate; and pentaacrylates, such asdipentaerythritol; and/or (monohydroxy) pentaacrylate.

A fifth Component (E) may optionally be included in some embodiments ofthe present composition. The fifth Component (E) may serve a variety ofdifferent purposes. In one embodiment, the fifth Component (E) may be adiluent such as an organic solvent and or water miscible organicsolvent. The compositions of this invention may optionally include adiluent selected from the group consisting of isopropanol, t-butanol,n-propanol, n-butanol, methanol, ethanol, ethylene glycol n-butyl ether,and mixtures thereof. Other diluents may also be used as long as adiluent selected from the aforementioned group may be present in anamount of at least 17 percent, based on the total amount of diluents inthe composition. Other embodiments may have lower concentrations.

Optionally, the fifth Component (E) may be an anaerobic gelationinhibitor such as but not limited to 2,2,6,6-tetramethylpiperidinyloxy,4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy,bis(4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy sebacate diradical,2,2-diphenyl-1-picrylhydrazyl, 1,3,5-triphenylverdazyl,1-nitroso-2-naphthol, or a nitrone. Such an inhibitor may beparticularly useful in a solventless composition. In alternativeembodiments, methylhydroquinone, galvinoxyl,4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy, N-t-butyl-a-phenyl nitrone,and/or 2,2-diphenyl-1-picryl-hydrazyl hydrate (DPPH) may be used asgelation inhibitors.

Still other embodiments of the present invention may use a Component (E)comprised of a hindered amine derivative. One such derivative isavailable from Ciba-Geigy Corporation under the trade name Tinuvin123.The hindered amine light stabilizers and UV absorbers may be useful asadditives to the present coating composition. Hindered amine lightstabilizers and UV absorbers act to diminish the harmful effects of UVradiation on the final cured product and thereby enhance theweatherability, or resistance to cracking, yellowing and delamination ofthe coating. A preferred hindered amine light stabilizer isbis(1,2,2,6,6-pentamethyl-4-piperidinyl)[3,5-bis(1,1-dimethylethyl-4-hydroxyphenyl)methyl]butylpropanedioate, available as Tinuvin®144, fromCIBA-GEIGY Corporation, Hawthorne, N.Y. A preferred UV absorber is2,2′4,4′-tetrahydroxybenzophenone, available as Uvinul® D-50, from BASFWyandotte Inc., Parsippany, N.J.

It should be understood that the ratio of components in the compositionmay vary. In one embodiment, the composition may have components in thefollowing ranges: Component A 30-60%, Component B 10-30%, ComponentC5-10%, and Component D 10-30%. In another embodiment, the compositionmay have components in the following ranges: Component A 30-60%,Component B 10-30%, Component C5-10%, Component D 10-30%, and ComponentE 10-30%.

In one embodiment, the hardcoat composition includes between 2 at. %silicon, 32 at. % carbon, 48 at % hydrogen, and 17 at % oxygen. Inanother embodiment, the composition may have 1-4 at % silicon, 20-40 at% carbon, 10-30 at % oxygen, and the balance made up by hydrogen. Insome embodiments, the amount of hydrogen may be in the range of about40-60 at %.

Although not limited to the following, in some embodiments, theprotective layer from the hardcoat may be in the range of about 1 toabout 500 microns in thickness. Some may have thickness less than 1micron. In other embodiments, the protective layer may be in the rangeof about 50 to about 300 microns. In other embodiments, the protectivelayer may be in the range of about 50 to about 150 microns. In otherembodiments, the protective layer may be in the range of about 75 toabout 100 microns. Of course, it should be understood that more than oneprotective layer may optionally be applied to each cell. Someembodiments may further include an anti-reflective layer above theprotective layer. In some embodiments, the protective layer may haveanti-reflective qualities.

By way of nonlimiting example, some commercially available hardcoatsadaptable for use with the present invention are listed blow. A numberof heat curable or UV curable silane prepolymer compositions arecommercially available from Wacker Silicones Corporation of Adrian,Mich.; Tego Chemie Service USA of Hopewell, Va.; and GE Silicones ofWaterford N.Y. As nonlimiting examples, heat curable silane prepolymercompositions are available from GE Silicones under the trade names SCH1200, AS 4000, LHC 100 and SHC 1010. Another heat curable silicone hardcoat is available from Nippon Dacro Shamrock Co., Ltd. under the tradename SolGard. These silane prepolymers may be applied by a variety ofmethods including but not limited to dip, flow, spray, electrostatic orspin coating. Substrates treated with these silane prepolymers may beallowed to dry at room temperature until tack free (15 to 20 minutes).Depending upon the specific silane prepolymer employed, the coatedsubstrates are then heated to a temperature greater than about 30° C. inorder to cure the prepolymer and form the polyorgano-siloxane clear coatlayer.

A variety of commercially available UV curable materials may also beused with the present invention. Some suitable UV curable silaneprepolymer compositions are available from Shin-Etsu Chemical Co., Ltd.under the trade names X-12, X-12-2206, X-12-2400, and X-12-2450; fromNippon Kayaku Co., Ltd. under the trade name Kayanova FOP; from WackerSilicones under the trade name Wacker F series and Wacker F-737; from GESilicones under the trade name UVHC series; from To a Gosei ChemicalIndustry Co., Ltd. under the trade names Aronix UV, Aronix UV-3033 andAronix UV-3700; from Shin Nakamura Chemical Company and To a GoseiChemical Industry Co., a mixture of compounds under the trade namesNK-Oglio-U4H and Aronix TO-1429; and from Tego Chemie Service (adivision of Degussa Corporation) under the trade names Tego SiliconeAcrylate 704, Tego Silicone Acrylate 705, Tego Silicone Acrylate 706,Tego Silicone Acrylate 707, Tego Silicone Acrylate 725, and TegoSilicone Acrylate 726. Other suitable protective materials may beavailable from Rohm & Haas Company under the trade name LS123; from theStanley Electric Co. Ltd. under the trade names SH2, SH41, and SH50;from Mitsubishi Rayon Co. Ltd. under the trade names Acryking, AcrykingPH350, and Acryking PH511; from Fujikura Kasi Co. Ltd. under the tradenames Fujihard 2500 and Fujihard 2551; and Red Spot Pain & Varnish Co.Inc. under the trade names UVT-200.

Optionally, still other types of hardcoat materials may be also beadapted for use with the present invention. Dai Nippon Printing Co. Ltd.(DNP) in conjunction with Fuji Photo Film Co., Ltd. (FujiFilm) havedeveloped various hardcoat films suitable for use with the presentinvention. InteliCoat Technologies provides a flexible,abrasion-resistant optically clear hardcoat films available under thetrade name StratFX. 3M provides hardcoat films under the trade nameVikuiti™. Targray supplies a UV-curable transparent hardcoat (Hardcoat#71) which provides a very hard scratch-resistant layer of 3-5 μm withexcellent optical properties. Lintec Corporation has developed apolycarbonate film under the trade name Opteria that combines a hardcoat and pressure-sensitive adhesive. Details of such a hardcoat arefound in US Patent Publication 20040081831 fully incorporated herein byreference. Teijin Chemical also provides a polycarbonate hardcoat filmunder the trade name PureAce. TDK Corporation provides a clear polymercoating under the trade name Durabis. Details of such a hardcoat may befound in US Patent Publications 20050095432 and 20050123741, both fullyincorporated herein by reference. Vitrinite® available from MetrolineIndustries, Inc. may also possess the desired protective properties.

Substantially Inorganic Protective Layer

Referring now to FIG. 4, it should be understood that a variety ofinorganic or substantially inorganic materials may also be suitable foruse as the protective layer 20 shown in FIG. 1, in addition to or inplace of, the substantially organic protective layers. In one embodimentas shown in FIG. 4, one material suitable for use as a protective layeris alumina. Other inorganic materials suitable for coating the cell 10include, but are not limited to, silica, aluminosilicates, diamond-likefilms, borosilicates, silicon nitride, aluminophosphosilicates,aluminophosphates, and/or combinations thereof. Other inorganicmaterials may also be suitable if they can provide a sufficient moisturebarrier and are sufficiently transparent to allow light to reach theabsorber layer of the solar cell 10. By way of nonlimiting example,other suitable materials may include Niobium oxide (Nb₂O₅), Niobiumnitride (NbN), Zirconium Oxide (ZrO₂), Zirconium Nitride (ZrN), HafniumOxide (HfO₂), Hafnium nitride (HfN), Zinc oxide (ZnO), Yttrium oxide(Y₂O₃), Cerium Oxide (CeO₂), Scandium Oxide (Sc₂O₃), Erbium oxide(Er₂O₃), Tantalum oxide (Ta₂O₅), Tantalum nitride (TaNx), Vanadium oxide(V₂O₅), Indium Oxide (In₂O₃), Aluminum nitride (AlN), Titanium Nitride(TiN), Molybdenum nitride (MoN), Gallium nitride (GaN), Lanthanum oxide(La₂O₃), Zinc Sulfide (ZnS), Tin oxide (SnO₂), strontium sulfide (SrS),calcium sulfide (CaS), lead sulfide (PbS), and/or combinations thereof.Of course, the protective layer 20 may be formed on the cells, the cellstrings, or the solar cell module.

As seen in FIG. 4, a protective layer 20 of alumina can been establishedvia a variety of processes including but not limited to atomic layerdeposition (ALD). Extraordinarily complete kinetic barrier propertiesmay be found when a plurality of atomic layers of low-defect ALDdeposited material is used. Some embodiments may have 50 or more layers.Some embodiments may have 80 or more layers. Some embodiments may have100 or more layers. Some embodiments may have 1000 or more layers. Thetotal thickness of the resulting ALD barrier may be in the range ofabout 100 to about 1000 angstroms. Some embodiments may have rangesbetween 200-800 angstroms. Some embodiments may have ranges between200-500 angstroms. Other embodiments may have a range of 250-350angstroms.

It should be understood that ALD process typically comprises of a seriesof half-reactions to deposit the monolayers. There are generally twotypes of reactions to form a metal oxide layer via the ALD process. In afirst type of ALD reaction, the process comprises of the repeatedapplication of organometallic precursor material and water to the targetsurface. In a second type of ALD reaction, the process comprises of therepeated application of a metal halide precursor material and water tothe target surface.

As an example of the first type of reaction, depositing a layer ofalumina over the solar cell 10 comprises of alternating exposure of thecell 10 to Al(CH₃)₃ and H₂O to form the ALD monolayers. Reactions usingAl(CH₃)₃ are preferably conducted in chamber(s) with sufficientstructural strength to withstand any highly exothermic or rapidcombustion reactions associated with the material. The ALD halfreactions may be summarized as:

Al—OH*+Al(CH₃)₃→Al—O—Al(CH₃)₂+CH₄  1)

Al—CH₃*+H₂O→Al—OH*+CH₄  2)

The asterisk indicates which material is on the substrate. It is alsounderstood that the second methyl —CH₃ group in the first half-reactionproduct is removed in a similar reaction step to that shown in thesecond half-reaction.

In another nonlimiting example of the first reaction type,tris(diethylamino) aluminum Al(NEt₂)₃ and/ortris(di-isopropylamino)aluminum may be used as precursors with water asa co-reactant in an ALD deposition process. Details can be found incopending U.S. Patent Publication US20050003662 to Jurisch et al., fullyincorporated herein by reference for all purposes.

As an example of the second type of reaction, layers of silica maydeposited over the cell 10 by alternating exposure of the cell 10 toSiCl₄ and H₂O to form the ALD monolayers. The ALD half reactions may becomprised of:

SiOH*+SiCl₄→SiO—Si—Cl₃*+HCl  1)

Si—Cl*+H₂O→Si—OH*+HCl  2)

In another nonlimiting example, layers of titania may deposited over thecell 10 by alternating exposure of the cell 10 to TiCl₄ and H₂O to fromthe ALD monolayers.

TiOH*+TiCl₄→TiO—Ti—Cl₃*+HCl  1)

Ti—Cl*+H₂O→Ti—OH*+HCl  2)

Details on various other ALD half reactions such as from halnium oxidecan be found with reference to Widjaja, Y. Musgrave, C. B. “Atomic layerdeposition of hafnium oxide: A detailed reaction mechanism from firstprinciples” Journal of Chemical Physics, 2002, VOL 117; PART 5, pages1931-1934, fully incorporated herein by reference for all purposes.Methods of forming hafnium oxide, zirconium oxide and nanolaminates ofhafnium oxide and zirconium oxide can be found in U.S. Pat. No.6,420,279 to Ono, et al., fully incorporated herein by reference for allpurposes.

Various modifications may be made to decrease the processing temperatureassociated with typical ALD processes. Some of these typical ALDprocesses may operate at temperatures >100-300° C. The use of materialssuch as but not limited to a Lewis base catalyst may allow fordeposition of ALD monolayers at significantly reduced temperatures. Asone nonlimiting example, a catalyst such as pyridine or ammonia may beused to reduce the processing temperature. In some embodiments, the ALDprocessing temperature can be lowered to as low as room temperature.Details on techniques for lowering ALD processing temperature can befound in J. W. Klaus and S. M. George, “Atomic Layer Deposition of SiO2at Room Temperature Using NH3-Catalyzed Sequential Surface Reactions”,Surf. Sci. 447, 81-90 (2000). Details on applying ALD alumina overpolymers can be found in J. D. Ferguson, A. W. Weimer, S. M. George,“Atomic Layer Deposition of Al2O3 Films on Polyethylene Particles” Chem.Mater. 16, 5602-5609 (2004). Details on techniques for using ALD layersas a wear-resistant coating can be found in T. M. Mayer, J. W. Elam, S.M. George and P. G. Kotula, “Atomic Layer Deposition of Wear-ResistantCoatings for Micromechanical Devices”, Appl. Phys. Lett. 82, 2883-2885(2003). All of the aforementioned publications are fully incorporatedherein by reference for all purposes.

Furthermore, different types of ALD techniques may be used to achievehigh throughput processing. By way of nonlimiting example, this mayinvolve batch ALD processing of a plurality of solar cellssimultaneously. Alternatively, high throughput ALD processing using acoiled support may be used to process a plurality of cells on anelongated substrate using a technique detailed in U.S. patentapplication Ser. No. 10/782,545 filed Feb. 19, 2004 and fullyincorporated herein by reference for all purposes.

M. D. Groner, et al., in the journal Applied Physics Letters, vol. 88,p. 051907 (2006), demonstrated that the water vapor permeability of afoil of poly(ethylene naphthalate), or PEN, is reduced at least 10,000×by a layer of 10 nm of alumina deposited by ALD. The final value of˜10⁻³ g/m²/day is sufficiently low to be a valuable barrier for theprotection of CIGS solar cells. The deposition temperature used in theseexperiments was 125° C. Even lower temperatures appear useful. Theprotective layer 20 provides the hermetic seal that eliminates the edgepermeation problem.

In another embodiment of the present invention, the protective layer 20has also been shown to work with a combination of alumina ALD followedby silica ALD or vice versa. This combination will have slightlyenhanced performance because silica is even less reactive with waterthan alumina. Combinations of inorganic materials may also be possiblesuch as but not limited to, hafnium oxide/tantalum oxide, titaniumoxide/tantalum oxide, titania/alumina, zinc sulfide/alumina, ATO, AlTiO,and/or combinations thereof. Nanolaminates may also be formed using theforgoing material combinations. U.S. Pat. No. 6,420,279 to Ono, et al.,fully incorporated herein by reference for all purposes also teachesformation of such nanolaminates. Optionally, some embodiments mayinclude any ALD deposited layer followed by coating via solutiondeposited layer such as but not limited to hardcoat material aspreviously discussed. Of course, some embodiments may place a hardcoatmaterial over the target surface followed by coverage by any offoregoing ALD deposited layers. The layer of alumina may be in the rangeof about 100 to about 1000 angstroms. Some embodiments may have rangesbetween 200-500 angstroms. Other embodiments may have a range of 250-350angstroms. In addition to that, the layer of silica used with thealumina may be in the range of about 100 to about 1000 angstroms. Someembodiments may have ranges between 200-500 angstroms. Other embodimentsmay have a range of 250-350 angstroms.

In some embodiments of the present invention, it may be advantageous ifthe protective layer 20 is deposited after the cells have been connectedin a series string, so that the only protrusion from the coating iscomprised of the tabbing metal which is used to connect the string tothe next string in the module.

A further advantage of the protective layer 20 is that it protects thesurface of the cell against mechanical damage during handling as it isbeing put into a module. Even though it is very thin, a layer of aluminais quite hard, and is therefore a more effective protective layer thanthe TCO.

A still further embodiment of the present invention may add a thincapping layer 23 above the protective layer 20 to protect the underlyinglayers. The capping layer 23 may be between about 5 to about 10angstroms in thickness. In other embodiments, the capping layers may bebetween 1 to about 20 angstroms in thickness. The capping layer 23 mayhave a material selected from one or more of the following: Niobiumoxide (Nb₂O₅), Niobium nitride (NbN), Zirconium Oxide (ZrO₂), ZirconiumNitride (ZrN), Hafnium Oxide (HfO₂), Hafnium nitride (HfN), Zinc oxide(ZnO), Yttrium oxide (Y₂O₃), Cerium Oxide (CeO₂), Scandium Oxide(Sc₂O₃), Erbium oxide (Er₂O₃), Tantalum oxide (Ta₂O₅), Tantalum nitride(TaNx), Vanadium oxide (V₂O₅), Indium Oxide (In₂O₃), Aluminum nitride(AlN), Titanium Nitride (TiN), Molybdenum nitride (MoN), Gallium nitride(GaN), Lanthanum oxide (La₂O₃), Zinc Sulfide (ZnS), Tin oxide (SnO₂),strontium sulfide (SrS), calcium sulfide (CaS), and lead sulfide (PbS).

The described barrier layer also has desirable dielectric properties.Because of the high quality (density, uniformity and low polarity) ofthe material, its insulating qualities are equivalent to much thickerlayers of encapsulating polymers such as EVA (whose resistivity is˜1000× lower than the best polymer insulators). Thus, the amount ofencapsulant polymer can be reduced, saving cost, and the cells can beplaced closer together, thereby increasing the efficiency of the module.

Referring now to FIGS. 5A and 5B, the present invention also disclosesother, non-ALD methods of providing a substantially inorganic protectivelayer for flexible solar cells which has good barrier properties,mechanical toughness, and stability under UV irradiation. It should beunderstood that various other vacuum based processes such as but notlimited to cyclical layer deposition, chemical vapor deposition (CVD),physical vapor deposition (PVD), plasma enhanced chemical vapordeposition (PECVD), and other deposition techniques may be used. Othernon-vacuum based deposition techniques may also be adapted for use withthe present invention.

In one embodiment of a non-vacuum deposition technique as seen in FIG.5A, an unfused barrier layer 70 is comprised of silica particles 72(shown more clearly in the enlarged portion of FIG. 5A), which may havenanometer scale dimensions, which are fused to form a good barrier. Theunderlying photovoltaic cells 74 may be stand alone device or devicessupported on a support layer 76 (shown in phantom). It should beunderstood that for any of the embodiments herein, the cells 10 may beindividually encapsulated or they may be mounted on a support and thenencapsulated. If the particles 72 are spherical (or approximately so),and of submicron diameter, then they touch in many places, and even asmall degree of fusing (not enough to eliminate all free volume) issufficient to create a long, tortuous path for diffusing gas molecules.

Referring to FIG. 5B, the fusing of particles 72 results in the fusedbarrier film 80, and this may be accomplished by several methods. Onemethod is by application of a short, intense pulse of heat (from alaser, for example), which is short enough so that heating and coolingtake place on a microsecond or shorter time scale, and this time isinsufficient for chemical damage to occur to an underlying layer. Suchshort-pulse thermal treatment has been applied to the recrystallizationof silicon on polymer films, for example, as described in U.S. Pat. No.5,346,850 issued to J. L. Kaschmitter, et al.

A second method is by the decomposition of a soluble precursor of silica(or a similar inorganic dielectric material) into which the particleshave been dispersed. Spin on glass (SOG) precursors such asdimethylsiloxane may be used, for example. With a high particle loadingof the dispersion, a coating can be made in which the particles occupymost of the volume, while the fluid occupies the interstitial volume anda thin coating on the particles. When this film is heated to decomposethe SOG precursor, the space not originally occupied by solid silicaspheres or other particles is now occupied by SOG which is ofsufficiently low permeability to severely impede the diffusion of vapormolecules through the small cross-section paths in between particles.

A third method is by the decomposition of vapor phase precursors,especially in a high-density plasma such as described by J. R. Sheats,et al., in U.S. Pat. No. 6,146,225, issued Nov. 14, 2000, entitled“Transparent, flexible permeability barrier for organicelectroluminescent devices”. Such plasmas enable the deposition of densedielectric films at low temperatures. When combined with a pre-existinglayer of silica (or other dielectric) nanoparticles, theplasma-deposited film can fill in the interstitial spaces with a denseand highly impermeable material. The combination of the two materialsresults in a much faster and more economical process since the majorityof the volume is occupied by the particles and this volume does not haveto be deposited by the relatively slow and expensive plasma process.

In addition to the methods of solution precursor deposition and plasmaprocessing previously described, a further preferred embodiment makesuse of atmospheric plasma chemical vapor deposition, using equipmentthat is sold for example by Surfx Technologies LLC, 3617 Hayden Avenue,Culver City, Calif. 90232. Silica films can be deposited by thistechnique over large areas at substantially higher rates than withconventional plasma enhanced chemical vapor deposition (PECVD), withlower cost due to the absence of need for vacuum.

Organic/Inorganic Hybrid Protective Layer

Referring now to FIGS. 6 and 7, it should be understood that a stillfurther type of material may be used for the protective layer 20 ofFIG. 1. In one embodiment as shown in FIG. 6, one suitable material maybe a hybrid material that forms a plurality nanolaminate layers.Specifically, the device may use an inorganic/organic hybrid barriernanolaminate film 100. Although the film 100 may be configured to coverall sides of the solar cell 10, FIG. 6 shows that the protective film100 may also be configured to selectively cover only the top and sidesof the solar cell 10. Optionally, still further embodiments may onlycover a top surface of the solar cell 10 that receives sun light.

Referring now to FIG. 7, the protective film 100 will be described infurther detail. The film 100 generally includes multiple alternatinglayers 102 of organic material and layers 104 of inorganic material.These layers may be covalently bonded layers, having covalent bondsbetween material in the organic layer 102 and material in an adjacentinorganic layer 104. The adjacent organic layers and inorganic layersmay be covalently bonded layers characterized by direct organicpolymer-inorganic material covalent bonds. The thickness of theinorganic layers 102 and organic layers 104 can be from about 0.1 nm toabout 1 nm or from about 1 nm to about 10 nm or from about 1 nm to about100 nm. The inorganic layers 102 can be silicates, although otherinorganic materials can be formed from suitable alkoxides as describedbelow. In some embodiments, the inorganic layers 102 may befunctionalized inorganic layers. The protective film 100 can be madesubstantially transparent by appropriate choice of the number,thickness, and composition of the inorganic layers 102 and organiclayers 104. The organic layers 104 may be polymers such as polyethylenenaphthalate (PEN), polyether etherketone (PEEK), or polyether sulfone.In addition, polymers created from styrene polymer precursors, methylstyrene polymer precursors, (meth)acrylate polymer precursors, bothfluorinated and non-fluorinated forms of these precursors, andcombinations of two or more of these precursors can be used as theorganic layers 104. Other suitable materials can be found in commonlyassigned, copending U.S. patent application Ser. No. 10/698,988 filedOct. 21, 2003 which is fully incorporated herein by reference.

Although a relatively small number of layers are shown in FIG. 7 for thesake of clarity, a barrier film for a typical device can have many morelayers, e.g., several thousand. The multi-layer structure of the barrierfilm 100 provides a long path for water or oxygen to penetrate thebarrier film to an underlying substrate 106, e.g., via pinholes and/orgaps at interfaces between layers as indicated by the path 108. Thepermeability of the nanolaminate barrier film 100 to oxygen and watervapor can be adjusted by changing the number of layers. By usinghundreds to thousands of interdigitated inorganic layers 102 and organiclayers 104 within the barrier film 100, the large number of layerscombined with randomly located pinholes within the nanolaminate resultsin tortuous paths for molecules such as water vapor and oxygen thatmight enter from the environment outside of the barrier film 100. Themore layers, the more tortuous the path for permeating molecules. Thus,the more layers, the less permeable the barrier film 100 is to watervapor and oxygen. In embodiments of the present invention, there can be100 or more, 1000 or more, 10,000 or more or 100,000 or more individuallayers in the composite barrier film 100.

By suitable choice of the number and composition of layers, the oxygenpermeability of the barrier film 100 can be made less than about 1cc/m²/day, 0.1 cc/m²/day, 0.01 cc/m²/day, 10⁻³ cc/m²/day, 10⁻⁴cc/m²/day, 10⁻⁵ cc/m²/day, 10⁻⁶ cc/m²/day, or 10 ⁻⁷ cc/m²/day.Similarly, the water vapor permeability of the barrier film 100 can bemade less than about 1 g/m²/day, 0.1 g/m²/day, 0.01 g/m²/day, 10⁻³g/m²/day, 10⁻⁴ g/m²/day, 10⁻⁵ g/m²/day, 10⁻⁶ g/m²/day, or 10⁻⁷ g/m²/day.In one embodiment, the water vapor permeability barrier is 10⁻³ g/m²/dayor better (i.e. less permeable). In another embodiment, the water vaporpermeability barrier is 10⁻⁴ g/m²/day or better (i.e. less permeable).

The nanolaminate barrier film 100 can be made in a single-step or in amultiple-step process by self-assembly using sol-gel techniques.Self-assembly of nanocomposite materials using sol-gel techniques isdescribed, e.g., in U.S. Pat. No. 6,264,741 to Brinker et al., theentire contents of which are incorporated by reference. The substrate106 can optionally be coated with the sol mixture by any suitabletechnique, such as dip coating, spin coating, spray coating, webcoating, or microgravure web coating. Suitable coating machines arecommercially available, e.g., from Faustel, Inc., of Germantown, Wis. Inparticular, a Continuous Coater Type BA from Werner Mathis AG of Zurich,Switzerland may be used to coat the substrate with the sol mixture. Itis desirable to coat the substrate with the sol in a wet layerapproximately 1 microns to 10 microns to 100 microns thick. Thicker wetlayers, e.g., about 100 microns to about 1 millimeter thick, can also beused. Since the barrier film 100 can be fabricated without the use ofvacuum equipment, the processing is simple and comparatively low incost.

The resulting nanocomposite structure in the multi-layer film isstabilized by (a) organic polymerization, (b) inorganic polymerization,and (c) covalent bonding at the organic interfacial surfaces. A singlecoating step can produce films at least 1000 nm thick comprised ofindividual layers, each roughly 1 nm thick. By taking advantage of theself-assembling nature of the materials, each set of 1000 layers can beformed in only seconds. A greater number of layers in the resultingbarrier film can be obtained by repeating the coating and evaporationsequence multiple times and/or by depositing thicker coatings.

Referring now to FIG. 8, a still further embodiment of the presentinvention comprising of a templated/waveguide barrier layer will now bedescribed. The nanolaminate barrier film 100 described above istypically configured as a plurality of horizontal layers of silica andhorizontal layers of hydrophobic polymer. When contaminants such aswater or oxygen enter the nanolaminate, the movement of the contaminantmolecules occurs through randomly distributed pinholes in thesehorizontal layers.

As seen in FIG. 8, although such a film 100 is effective, barrierqualities of such a film may be further improved by creating a templatedbarrier film 120. The embodiment of the nanolaminate in FIG. 8 is formedas a templated nanolaminate barrier film 120 through the addition ofbeads 122. The beads 122 may be made from a variety of materialsincluding but not limited to silica, glass, or other transparentinorganic materials. The beads 122 may come in a variety of shapes suchas spherical, platelet, flake, or the like. The beads 122 as measured inthe direction of their largest dimension may be sized between about 1 nmto about 10 microns. In one embodiment, the beads 122 are all ofsubstantially uniform size. In other embodiments, the beads 122 aresized to be within 5-10% of each other. In still other embodiments, awide variety of bead sizes are used. The beads 122 are of submicronsizes in one embodiment.

The addition of beads 122 enhances the barrier qualities of the film byminimizing the tortuous paths passing through the film 120. Instead ofthe various tortuous paths leading through the film, the tortuous pathsin the film 120 lead toward the individual beads 122 which are dead-endpaths. With sufficiently high numbers of beads, contaminants will morelikely than not follow a tortuous path to a bead 122 instead of atortuous path that leads to the other side of the film 120. Thissignificantly improves the quality of the barrier since even if acontaminant traverses the tortuous path, the path fails to lead to theother side of the film 120.

FIG. 9 is an enlarged view showing the templated nanolaminate layer 120in more detail. As a nonlimiting example, one possible tortuous path 130is shown leading from an outer, concentric nanolaminate layer 132 to thebead 122. Very few paths if any lead through one side of the layer 122to the other side of the layer 122. Most paths will eventually encounterone of the many concentric layers 132 around the beads 122 and be leadtoward a dead-end instead of along a path through the layer 132.Additionally, areas 134 between coated nanolaminated glass beads 122(e.g. interstitial volume) may be non-templated nanolaminate (shown hereschematically) and not open voids.

By way of example and not limitation, the concentric nanolaminate layer132 may alternate between an inorganic layer and an organic layer. Inone embodiment, the nanolaminate layers 132 may be 1 nm thick layersalternating between layers of SiO2 and layers of hydrophobic polymer.Other self-assembled layers may have other configurations withvariations on the number of alternating layers.

The use of beads 122 in the templated nanolaminate will advantageouslyprovide at least some of the following benefits. As a nonlimitingexample, incorporation of solid glass beads 122 allows for higheraverage glass density in the overall film since bead glass will behigher density (2 g/cc) than sol-gel glass (1.7 g/cc). Additionally,unlike non-templated nanolaminate layers, templated nanolaminate filmwill drive contaminants such as water or oxygen vapor molecules from theoutside of the coating to the bead, where contaminant molecules becometrapped and cannot easily exit the film. Since the only way thecontaminant molecules can exit are through those same entry paths(molecular waveguides), and by exiting, they block further entry ofother molecules. Accordingly, the steady-state permeation rate will below on average throughout the structure. As a further advantage, thetortuous path length per unit coating volume should also increasethrough the use of the beads 122.

By way of example and not limitation, these beads 122 may be added tothe dispersion before, during, and/or after solution coating of thematerial for forming a nanolaminate film similar to that for formingfilm 120. With the beads 122 present during the self assembly process,the concentric nanolaminate layers may form around the beads 122 tocreate the templated nanolaminate barrier film 120. The beads 122 may bein the form of a dry powder and/or in a dispersion added to another drypowder, dispersion, and/or emulsion. The suspension may be applied overthe photovoltaic cells or other layer by any of a variety ofsolution-based coating techniques including, but not limited to, wetcoating, spray coating, spin coating, doctor blade coating, contactprinting, top feed reverse printing, bottom feed reverse printing,nozzle feed reverse printing, gravure printing, microgravure printing,reverse microgravure printing, comma direct printing, roller coating,slot die coating, meyerbar coating, lip direct coating, dual lip directcoating, capillary coating, ink jet printing, jet deposition, spraydeposition, and the like, as well as combinations of the above and/orrelated technologies. Optionally, it should be understood that the beadsare not limited to spherical shapes and may be particles having planar,oblong, or other shapes.

It should be understood that other types of barrier coatings, such asdescribed by J. D. Affinito and D. B. Hilliard in U.S. Appl. No.20050051763, “Nanophase multilayer barrier and process”, and by A. G.Erlat, et al., in the Proceedings of the SVC, 2005, pp. 116-120, and T.W. Kim, et al., US. Appl. No. 20060003189, “Barrier coatings”, may alsobe applied to the solar cell, the solar cell string, or the packaging.Additionally, multilayer composites such as those described by thetradename “ORMOCER” and developed by the Fraunhofer Institute forSilicate Research, Neunerplatz 2, Wuerzburg, Germany, and disclosed inU.S. Pat. No. 6,503,634 may be advantageously used. All of the abovereferenced publications are fully incorporated herein by reference.

Applying a Protective Layer to the Solar Cell

Referring now to FIG. 10, it should be understood that there are avariety of methods to form the protective layer over the solar cell 10.Step 200 shows that the solar cell or other photovoltaic device isformed. At step 202, the protective layer is formed over the solar cellor photovoltaic device. Some embodiments of the protective layers 20 maybe applied by ALD and other vacuum deposition processes. Optionally,other embodiments of the protective layers 20 may be formed by asolution deposition process. Solution depositing the material may becomprised of using at least one of the following techniques: wetcoating, spray coating, spin coating, doctor blade coating, contactprinting, top feed reverse printing, bottom feed reverse printing,nozzle feed reverse printing, gravure printing, microgravure printing,reverse microgravure printing, comma direct printing, roller coating,slot die coating, meyerbar coating, lip direct coating, dual lip directcoating, capillary coating, ink jet printing, jet deposition, spraydeposition, aerosol spray deposition, dip coating, web coating,microgravure web coating, or combinations thereof. The solutiondeposition process may be applied in a single coat or in multiple coats.This may address any imperfections that may be present in the layer ifonly one coat is applied. Any of the foregoing may be applied in aroll-to-roll process or in a batch process.

Optionally, in other embodiments, the protective layers 20, 100, and 120may be applied as pre-formed sheets that are laminated onto the solarcell 10. The protective layers 20, 100, and 120 may be applied in singleply sheets or multiple ply sheets. Optionally, more than one sheet maybe applied to each solar cell.

As seen in FIG. 10, the protective layers 20, 100, and 120 formed bysolution deposition may optionally be further processed to cure theprotection layer at step 204 (shown in phantom). The curing may involveultraviolet techniques, electron-bean irradiation techniques, otherradiation techniques, thermal techniques, or other curing techniques.

Referring now to FIG. 11, if an ultraviolet technique is used for curingthe protective layer, one or more ultraviolet lamps may be provided. Asseen in FIG. 11, the lamp 220 (and optionally a second lamp 222) maygenerate ultraviolet light having a wavelength in the range ofapproximately 300 nm to 400 nm since the effective wavelength spectrumfor curing one embodiment of the material may be in the 300 nm to 400 nmregion. Of course, wavelength spectrum of the lamp or lamps may bevaried to optimize curing of the material. The lamps 220 and 222 may besupported by and electrically connected to suitable fixtures. UV lightmay be provided with mercury vapor lamps from UVEXS, Inc. Model CCU orModel 912 curing chambers (Sunnyvale, Calif., U.S.A.). The lamp mayoptionally be a xenon, metallic halide, metallic arc, or high, medium,or low pressure mercury vapor discharge lamp. Of course, it should beunderstood that one or more lamps or UV sources may be used tofacilitate curing of the hardcoat composition. Any of the foregoing maybe applied in a roll-to-roll process or in a batch process.

Optionally, as seen in FIG. 10, the entire cell string 250 may be coatedwith a protective layer 20. FIG. 10 shows that the entire cell string250 may be lowered into a bath 252 of protective material as indicatedby arrow 254. The coated cell string 250 is then removed from the bathand the protective layer cured onto the cell string 250. Of course, anyof the other deposition techniques described herein may also be used,including: wet coating, spray coating, spin coating, doctor bladecoating, contact printing, top feed reverse printing, bottom feedreverse printing, nozzle feed reverse printing, gravure printing,microgravure printing, reverse microgravure printing, comma directprinting, roller coating, slot die coating, meyerbar coating, lip directcoating, dual lip direct coating, capillary coating, ink-jet printing,jet deposition, spray deposition, aerosol spray deposition, dip coating,web coating, microgravure web coating, or combinations thereof. Thesolution deposition process may be applied in a single coat or inmultiple coats. This may address any imperfections that may be presentin the layer if only one coat is applied. Any of the foregoing may beapplied in a roll-to-roll process or in a batch process. Some assemblymethods may first individually coat each cell 10 and then coat theentire string 250 after the cells 10 are strung together. Optionally,the cells 10 are uncoated and then coated all at once as shown in theembodiment of FIG. 10.

Preferably, the solar cells 10 with the protective layer 20 will have awater vapor transmission rate (WVTR) sufficiently low so that there issubstantially no loss in solar cell conversion efficiency when the cellis exposed for 1000 hours at 85° C. and 85% relative humidity.Alternatively, the WVTR of the protective layer 20 is such that theconversion efficiency of a cell with the layer 20 has a conversionefficiency at least 25% better than an unprotected cell after both areexposed for 1000 hours at 85° C. and 85% relative humidity. In anotherembodiment, the cell with layer 20 has a conversion efficiency at least50% better than an unprotected cell after both are exposed for 1000hours at 85° C. and 85% relative humidity. In another embodiment, thecell with layer 20 has a conversion efficiency at least 75% better thanan unprotected cell after both are exposed for 1000 hours at 85° C. and85% relative humidity. In another embodiment, the cell with layer 20 hasa conversion efficiency at least 100% better than an unprotected cellafter both are exposed for 1000 hours at 85° C. and 85% relativehumidity.

Modules with Individually Encapsulated Solar Cells and/or Cell Strings

Referring now to FIG. 13, one embodiment of a module using encapsulatedsolar cells will now be described. FIG. 13 shows a plurality ofindividually encapsulated cells 10 mounted in the layer 300. If thelayer 300 is a rigid layer, it may involve mounting each of the solarcells 10 on a substrate such as but not limited to glass, soda-limeglass, steel, stainless steel, aluminum, polymer, ceramic, metal plates,metallized ceramic plates, metallized polymer plates, metallized glassplates, and mixtures thereof. The solar cells themselves may be flexibleor rigid. If the layer 300 is a flexible layer, the solar cells 10 maybe mounted on a flexible substrate such as but not limited to specialtythin, crack-resistant glass microsheet from Schott AG of Germany, coatedsteel foil (with a corrosion-resistant coating), stainless steel foil,aluminum foil, polymeric-material films, ceramic coatings on metal foilor polymer film, and combinations thereof. In some embodiments, thelayer 300 such as but not limited to aluminum foil or stainless steelfoil is electrically conductive and can be designed to have electricallyconductive diffusion barrier layers. This allows the layer 300 to carryelectrical current and reduce thickness of various layers used in thedevice. Again, the solar cells 10 themselves may be flexible or rigid.It should also be understood that the embodiment may use a superstrateor substrate configuration as understood by those skilled in the art.

Advantageously, because each solar cell may optionally be individuallyprotected, materials previously deemed unsuitable may be adapted for usewith the present invention. As seen in FIG. 13, because each solar cell10 in layer 300 is individually encapsulated, some embodiments of thepresent invention may use layers 310 and 312 with relaxed protectivequalities. By way of nonlimiting example, the layer 310 may be aflexible layer that may have enhanced scratch resistance but reducedmoisture barrier properties. Optionally, in another embodiment, themoisture barrier properties of layer 310 are enhanced while scratchresistance may be reduced. Optionally, the edge tape 54 may be left offsince the cells themselves are individually encapsulated. Optionally,the layer 310 may be a rigid layer of reduced thickness to reduce thematerials cost for each module.

Referring now to FIG. 14, embodiments of the present invention mayprovide improved configurations that add further protective capabilitiesto the embodiments shown in FIG. 13. FIG. 14 shows that a pluralityindividually encapsulated solar cells 10 in a multi-ply module packagingthat may allow for best in class materials to be used. Although notlimited to the following, it should be understood that the substantiallyorganic material, substantially inorganic material, hybridorganic/inorganic material, and the various techniques for applyingthose layers may be adapted for use to form the various module levelbarrier and/or encapsulant layers for FIGS. 13 and 14.

As seen in FIG. 14, a multi-ply encapsulant layer 320 is shown at aposition above the photovoltaic layer 300. In this position above thephotovoltaic layer 300, the encapsulant layer 320 is of sufficienttransparency to allow light to pass through the multi-ply layer 320 toreach the photovoltaic layer 300. In the embodiment shown in FIG. 12,the encapsulant layer 320 may be comprised of a plurality of individuallayers 322, 324, and 326. It should be understood that some embodimentsof the present invention may use an encapsulant layer 320 comprised ofonly two layers. In other embodiments, the encapsulant layer 320 may becomprised of four layers or more. In the present embodiment, the layers322, 324, and 326 are preferably highly transparent to solar radiationover a wide range of wavelengths such as but not limited to visible,infrared, and/or near ultraviolet wavelengths. Optionally, the layers322, 324, and 326 may have a thickness and elastic range-of-motioncombination that enables flexibility for the encapsulant layer 320. As anonlimiting example, the layer 320 may have a flexibility sufficient toroll up on a round core of about 0.01 to about 2.0 m radius, about 0.02to about 1.0 m radius in another embodiment, and between about 0.06 toabout 0.5 m radius in yet another embodiment.

In one embodiment of the present invention, layer 322 may havereasonable scratch resistance. Although not limited to the following,scratch resistance can be quantified by the ASTM D3363 pencil scratchtest, where scratch resistance versus 1H, 2H, 3H, 4H, or harder pencilleads is desirable. Scratch resistance can also be quantified by theASTM D1044 Taber abraser test, where a grinding wheel of specifiedroughness, specified downward force, and specified number of rotationcycles is used to rub the surface under test. The amount of mass abradedaway or the optical haze induced by the abrasion is the measuredresponse to quantify scratch resistance. For a CS-10F test wheel with500 gram-force (4.9N) downward, it is preferable to have less than 10%optical haze after 50 wheel revolutions. Haze is measured per ASTMD1003.

The layer 322 may optionally be highly UV resistant. This may compriseof resistance to UV-induced embrittlement, powdering, chalking, anddiscoloration for certain periods of exposure. UV-test per UV exposurefrom a xenon arc lamp, such as embodied in the QUV instrument from QPanel Corp. The layer 322 may optionally have ultraviolet blockingability to protect one or more layers below the layer 322 or the toplayer in the encapsulant layer 320. As a nonlimiting example, the layer322 may comprise of a co-polymer of ethylene and tetrafluoroethylene(ETFE), or silica-nanoparticle-filled, UV-resistance-additive-containingacrylic scratch resistant hard coat rated at 2H, 3H, or 4H pencilscratch resistance, or a weatherable silicone-based hard coat. The ETFEmay be a modified ETFE (ethylene-tetrafluoroethylene) fluoropolymer suchas but not limited to Tefzel®.

The layer 324 may optionally include properties that might separate outthe function of either and/or both layer 322 or layer 326. The layer 324may optionally provide one or more of the following: good adhesionbetween layer 322 and layer 326; enhanced barrier properties todiffusion of water molecules or oxygen molecules; or enhancedultraviolet resistance; or provide better light transmission by havingan intermediate index of refraction that is between the indices ofrefraction of layers 322 and 326. As a nonlimiting example, the layer324 may be a difunctional molecular monolayer where one chemicalfunctional group bonds well to layer 322 and another chemical functionalgroup bonds well to layer 326. Optionally, the layer 324 may be a thinadhesive layer made from a version of layer 322 and/or a version oflayer 326 that has been modified to enhance the bonding of layer 322 andlayer 324. In other embodiments of the invention, the layer 324 may be athin-film (nanofilm) of a barrier material such as but not limited tosputtered silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), or othertransparent oxide, a hybrid inorganic-organic barrier coating, such asultra-high barrier coating which comprises silicon oxides, nitrides, andorganic Si containing plasma polymer with nondiscrete interfacesmarketed for organic light emitting displays (OLEDs). Layer 324 can alsoconsist of sublayers of alternating organic/inorganic barrier layers,such as Vitex Barix barrier layer marketed for OLEDs. In someembodiments, the layer 324 may include a notch filter layer to passwavelengths that are a subset of light wavelengths. The layer mayinclude a filter selected from one of the following to pass a desiredset of light wavelengths: bandpass filter, high-pass filter, or low-passfilter.

The layer 326 may optionally be a thermoplastic polyurethane, athermosetting ethylene vinyl acetate (EVA), a thermoplasticfluoropolymer such as a copolymer of tetrafluoroethylene,hexafluoropropylene and vinylidene fluoride (THV), a silicone basedmaterial, and/or a thermoplastic ionomer resin such as but not limitedto DuPont Surlyn®. In one embodiment, the layer 326 comprises of athermoplastic polyurethane such as but not limited to Desmopan®aliphatic ester thermoplastic polyurethane from Bayer or Dureflex® A4700aliphatic ether thermoplastic polyurethane from Deerfield Urethane. TheA4700 properties include a nominal Shore A hardness of 78 measured perASTM D2240, specific gravity of 1.08 measured per ASTM D792, a nominal100% elongation modulus of 3.5 MPa measured per ASTM D882, a nominaltear resistance of 4.37 N/mm measured per ASTM D1004, an optical hazebelow 1% on Hazegard instrument per ASTM D1003-61. Other materials withsimilar performance qualities in the range of those listed above (+/−within about 5% to 10%) may of course be used in place of and/or incombination with those listed above. The thickness of layer 326 isbetween 10 microns and 1000 microns, between 10 microns and 500 micronsin another embodiment, and between 100 and 300 microns in a stillfurther embodiment.

It should be understood that the multi-ply encapsulant layer 320 is notlimited to the layers shown in FIG. 14. Other embodiments of themulti-ply encapsulant layer 320 may include additional layers ofmaterial to add additional protective qualities. Other embodiments ofthe encapsulant layer 320 may include additional layers of the samematerials or may be layers of different materials than those found inlayers 322, 324, and/or 326. The layers may also be used with edge tape54 as suitable.

Referring still to FIG. 14, a multi-ply encapsulant layer 350 may becoupled to an underside of the photovoltaic layer 300. FIG. 14 showsthat the encapsulant layer 350 may also comprise of a plurality oflayers of materials. Some embodiments of the encapsulant layer 350 maycomprise of more than those shown in FIG. 14. It should also beunderstood that some embodiments may have fewer layers. As a nonlimitingexample, FIG. 12 shows that the encapsulant layer 350 may also compriseof layers 352, 354, and 356. Optionally, some embodiments may only havetwo discrete layers. Others may have four or more discrete layers thatbond together to form encapsulant layer 350. In one embodiment of thepresent invention, layer 352 may be an opaque version of one of thematerials used in layer 356. Optionally, it may be a lower cost materialwith opaqueness or reduced UV-resistance properties.

Layer 354 may be one of materials suitable for use in layer 324 oradditionally it can be an opaque version of layer 324. Such an opaquelayer may be created by adding a pigment selected from the followinglist: carbon black, titanium dioxide, or any stable inorganic pigment.In another embodiment, the layer may be a lower cost material withopaqueness or reduced UV-resistance properties, such as but not limitedto aluminum foil, stainless steel foil, other types of metal foils.

Layer 356 may be one of the materials suitable for use in layers 322 and324 or additionally it can be an opaque version of layer 322 and layer324 materials. In one nonlimiting example, layer 356 may be selectedfrom the following example conventional back sheets:Tedlar®-polyester-Tedlar® (TPT), Tedlar®-polyester (TP),Tedlar®-aluminum-polyester (TAP), Tedlar®-aluminum-polyester-Tedlar®(TAPT), Tedlar®-aluminum-polyester-EVA (TAPE). These conventional backsheets also contain adhesive tie layers and adhesion-promoting surfacetreatments that are proprietary to the back sheet vendors. Conventionalback sheets are available from Isovolta of Austria and Madico of USA.Layer 356 may optionally be selected from the following exampleunconventional back sheets: aluminum sheet; galvanized steel; Galvalume®55% aluminum-zinc alloy coated sheet steel; conversion-coated steel suchas chromate-based, phosphate-based, or similar corrosion-resistantcoated sheet steel; plasticized or unplasticized polyvinylchloride (PVC)formulations; aliphatic ether or aliphatic ester or aromatic ether oraromatic ester thermoplastic polyurethanes; ethylene-propylene-diene(EPDM) rubber sheet; thermoplastic polyolefin (TPO) sheet, polypropylenesheet, polyethylene sheet, polycarbonate sheet, acrylic sheet, and/orsingle or multiple combinations thereof.

It should be understood that a variety of processes may be used to formthe various protective layers on the photovoltaic layer 300. The layersmay be integrally formed, dipped, coated, solution deposited, laminated,otherwise formed, or any single or multiple combinations thereof. Onemode of lamination for EVA encapsulant is a vacuum lamination at about135 C, 1 atm pressure, for 10 to 30 minutes, a thermoset process. In aroll-to-roll process, the vacuum laminator may have either a continuousmotion or a step-and-repeat motion within to both match the productionline rate and the time required for EVA lamination.

One mode of lamination for TPU encapsulant and any other layer herein ishot nip lamination, where the high temperature and high pressure pair ofnip rolls quickly laminate the layers together. The temperature of thenip rolls is between 85° C. and 250° C., between 100° C. and 200° C. inanother embodiment, and between 125° C. and 200° C. in a still furtherembodiment. The pressure is indirectly defined through the nip rolldiameter, the deformation properties of the materials to be laminated,the downward force of the nip roll onto the materials to be laminated.The downward force is a combination of the weight of the nip roll, anyupward force from optional hard stops that prevent the nip roll frommoving downward past a certain point, any downward force applied byhydraulic or pneumatic cylinders with adjustable set points such as aregulator that down-regulates a compressed air supply to a certain airpressure. The appropriate pressure for a given set of materials andlamination speed is determined without undue experimentation by startingat zero cylinder force and increasing the force until air-bubble-freeadherent laminates are formed.

Manufacturing

A variety of techniques can be used to manufacture cells, cell strings,and/or solar cell modules with the protective layers described herein.The type of manufacturing and/or assembly technique may vary based onwhether the solar cell itself is a rigid device or a flexible device.

Referring now to FIG. 15, it should be understood that the embodimentsof the present invention may be suitable for use on a rigid substrate400. By way of nonlimiting example, the rigid substrate 400 may beglass, soda-lime glass, steel, stainless steel, aluminum, polymer,ceramic, coated polymer, or other rigid material suitable for use as asolar cell or solar module substrate. A high speed pick-and-place robot402 may be used to move rigid substrates 400 onto a processing area froma stack or other storage area. FIG. 13 shows how a pick-and-place robot410 may be used to position a plurality of rigid substrates on a carrierdevice 412 which may then be moved to a processing area as indicated byarrow 414. This allows for multiple substrates 400 to be loaded beforethey are all moved together to undergo processing. It should beunderstood that processing as described may be any of a variety ofprocesses. The processing may be to coat the individual cells in a batchprocess, to couple the individual cells into a string, to mountindividual cells onto a module or assembly, or to laminate the cells toa module or assembly.

Referring now to FIG. 16, it should also be understood that theembodiments of the present invention may be suitable for use on aflexible substrate in a roll-to-roll manufacturing process.Specifically, in a roll-to-roll manufacturing system 450, a flexiblesubstrate 451 travels from a supply roll 452 to a take-up roll 454. Inbetween the supply and take-up rolls, the substrate 451 passes a numberof applicators 405A, 456B, 456C, e.g. microgravure rollers, andprocessing units 458A, 458B, 458C. Each applicator deposits a layer orsub-layer as described above. The processing units may be used to cureeach layer and/or promote adhesion between layers. In the exampledepicted in FIG. 14, applicators 456A and 456B may apply differentsub-layers of the protective layer. Processing units 458A and 458B maycure each sub-layer before the next sub-layer is deposited.Alternatively, both sub-layers may be cured at the same time. Applicator456C may optionally apply an extra layer of material above the otherlayers. Processing unit 458C heats the optional layer and precursorlayer as described above. Note that it is also possible to sequentiallydeposit all layers together which is then cured or processed to form theprotective layer. The roll-to-roll system may be a continuousroll-to-roll and/or segmented roll-to-roll, and/or batch modeprocessing.

Referring now to FIG. 17, it should be understood that the presentinvention may also be well suited for module assembly via a variety ofprocesses including, but not limited to, a roll-to-roll process. Thephotovoltaic cells 512 themselves may be manufactured using aroll-to-roll process. The cells 512 may then be processed and assembledin strings of cells 512. Then, the assembly of a string of cells 512 andthe support substrate 520 may also be combined together using aroll-to-roll assembly process where rollers may be used to bring the twotogether as seen in FIG. 15. Optionally, a roll of support substrate 520may be unrolled and brought together with one or more strings ofphotovoltaic cells 512. Subsequently, the combined multi-layer assembly530 may enter a laminator to complete the assembly process. As anonlimiting example, one method of lamination for an EVA encapsulant foruse with the roofing assembly is vacuum lamination at about 135° C., 1atm pressure, for 10 to 30 minutes, in a thermoset process. In aroll-to-roll process, the vacuum laminator is a long piece of capitalequipment that has continuous or step and repeat motion within to matchthe production line rate with the time required for EVA lamination. Onemode of lamination for TPU encapsulant is hot nip lamination, where thehigh pressure and temperature rolls quickly laminate the layerstogether. The heating is to bring the TPU to a hot, soft state forbonding and post-nip cooling is to harden the encapsulant. Thisthermoplastic process is much faster than the EVA thermoset, on theorder of about 10× faster. The capital equipment for roll-to-roll niplamination is far smaller, simpler, and less costly than roll-to-rollthermoset vacuum lamination. This offsets the higher materials cost ofthe TPU versus EVA. The lamination process can also include thesimultaneous formation of cell-to-cell and cell-to-wiring electricalconnections. In this example, cells could be placed on an adjacent layerby a pick-and-place mechanism included in the roll-to-roll process.Other types of lamination suitable for use with the present inventioninclude flatbed roll-to-roll lamination (as provided by Glenro ofPaterson N.J.), press lamination, vacuum bag lamination, bathlamination, dip lamination, and/or combinations thereof.

Form Factors

Referring now to FIG. 18, the support substrate 520 may be a flexiblemembrane such as a roofing membrane that is combined with the cells 10or cell strings 512. The resulting photovoltaic roofing membrane 550with photovoltaic cells 512 may be rolled together and formed inelongated flexible sections of substantially uniform thicknessconstructed for being rolled up in lengths suitable for beingtransported to a building site for unrolling and for being affixed to aroof structure. As seen in FIG. 18, the flexible nature of thephotovoltaic cells 512 allows them to be rolled up with the roofingmembrane 520 without any special mechanical spacers, gaps, or structuralalterations found in known devices that use rigid photovoltaic cells. Inone embodiment, the rolls are between about 6.5 to about 10 feet wideprefabricated to cover up to the desired area to be covered by one roll.The area may be selected to cover only those areas that receiveunobstructed sunlight. In some embodiments, this may be a roll with anarea of about 2500 sq ft. In other embodiments, the area may be about3000 sq ft, 5000 sq ft, 10,000 sq ft, 50,000 sq ft, 100,000 sq ft ormore.

As seen in FIG. 18, the rolls formed by the flexible cells and theroofing membrane may have the cells deflecting between about 1 mm toabout 1000 mm radius of curvature, between about 5 mm to about 500 mm inanother embodiment, and between 10 mm to 100 mm in yet anotherembodiment, without damaging the cell. The ability of the cell todeflect allows the roofing membrane to be applied to the variouscontours and shapes on the rooftop without being limited by being aroofing membrane. The relative thinness of the photovoltaic cells alsoallows the rolls to be handled, rolled, unrolled, and transported withsubstantially the same equipment used to handle typical,non-photovoltaic roofing membranes.

Referring now to FIG. 19, the membrane 520 and photovoltaic cells 512may be contoured as desired to follow the shape of the underlyingsupport surface that the membrane 520 is mounted on. In FIG. 19, thismay be on curved tiles, flat metal plates, copper roofing member, or anyother suitable surface 570. These tiles or plates of surface 570 may beindividual, discrete elements or contiguous elements. It should beunderstood that in some embodiments, the membrane 520 may a lessweatherproof membrane and rely on the underlying support surface 570 toprovide weatherproofing capability. Optionally, a second layer ofmaterial 572 may be attached to the roofing membrane 520. The secondlayer 572 may be used to provide more structural support or it may beused to improve other qualities of the roofing membrane 520. The secondlayer 572 may be selected from a variety of materials including but notlimited to: photonic textiles, metallic yarns, metallized yarns,conductive polymers on fabrics, textile electronics, woven polymersincluding nylon, mylar (PET), extruded plastics, stamped metals plates,unstamped metal plates, or combinations thereof. Textiles are classifiedaccording to their component fibers into silk, wool, linen, cotton, suchsynthetic fibers as rayon, nylon, and polyesters, and some inorganicfibers, such as cloth of gold, glass fiber, and asbestos cloth. They arealso classified as to their structure or weave, according to the mannerin which warp and weft cross each other in the loom (see loom; weaving).Value or quality in textiles depends on several factors, such as thequality of the raw material used and the character of the yarn spun fromthe fibers, whether clean, smooth, fine, or coarse and whether hard,soft, or medium twisted. Density of weave and finishing processes arealso important elements in determining the quality of fabrics. GORE-TEX®expanded polytetrafluoroethylene (PTFE), Kevlar® polyaramid, Nylon®polyamide, Neoprene® polychoroprene, Spandex® elastomer, Velcro® hookand loop fastener, polyvinylchloride, and the like may also be used.Flax, cotton, silk, wool, lyocell, microfibers, microdenier, polyolefin,polypropylene, polyester, triacetate, rayon, acetate, and acrylic mayalso be used.

It should understood that the flexible membranes and solar cellsaccording to the present invention may be used in a variety of otherapplications such as building facades, tents, roofing tiles, cladding,tarps, awnings, window materials, and the like. Additional examples areset forth in commonly assigned, copending U.S. Provisional PatentApplication Ser. No. 60/804,570 (filed Jun. 12, 2006), 60/804,571 (filedJun. 12, 2006), and 60/746,626 (filed May 5, 2006), fully incorporatedherein by reference for all purposes.

While the invention has been described and illustrated with reference tocertain particular embodiments thereof, those skilled in the art willappreciate that various adaptations, changes, modifications,substitutions, deletions, or additions of procedures and protocols maybe made without departing from the spirit and scope of the invention.For example, with any of the above embodiments, other types oflamination suitable for use with the present invention include flatbedroll-to-roll lamination (as provided by Glenro of Paterson N.J.), presslamination, vacuum bag lamination, bath lamination, dip lamination, orany single or multiple combinations thereof. With any of the aboveembodiments, elements might be created in situ rather than pre-formed.With any of the above embodiments, elements might be partially createdat one stage in the process and finished later in the process. With anyof the above embodiments, the term foil can include both metallic foiland non-metallic foil. With any of the above embodiments, the term“rolled up” can include combinations of roll bends and other packingmethods such as folds, fanfolds, rounded folds, and rounded fanfolds.Some embodiments of the invention may not have all of the layers recitedabove. Some may have only multi-layers on the top side. Some may havemulti-layers on only the bottom side. Still other embodiments may havemulti-layers, but not as many as those shown. Others may have many morelayers than those shown. As a non-limiting example, layers 322, 324, and326 may be repeated on the top side to further improve the level ofprotection. Some may only repeat selected layers such as 324 and 326.Others may use thicker layers of one material such as top layer 322 forincreased protection. Other embodiments may have more layers betweenlayers 322 and 326 and not just one layer 324. The layers may all be ofdifferent material compositions. Others may have certain portions thathave alternating sets of layers that define a laminate layer. In oneembodiment, all topside layers are of sufficient transparency tominimize loss of light as light passes through the layers to reach aphotovoltaic cell. Other embodiments may not have the most scratchresistant layer as the outermost layer.

For any of the embodiments herein, the following may also apply. Interms of moisture barrier properties, the barrier to water may be lessthan 0.1 g/m2/day of water vapor permeation at 25 degrees C. and 50% RH,preferably less than 0.01, most preferably less than 0.001. In terms ofother barrier properties, barrier to ions may be less than 0.01 g/m2/dayof acetic acid permeation at 25 degrees C. where the acetic acid has aconcentration at the outer surface of the barrier layer of 10̂(−4)moles/liter. The barrier to ions is preferably less than 0.001 g/m2/day,most preferably less than 0.0001 g/m2/day. Some embodiments of a modulemay have all solar cells and/or cell strings with a protective layer. Inother embodiments, only some of the cells and/or cell strings have theprotective layer. Some may have more than one protective layer on atleast one of the cells and/or cell strings. The protective layer may besuch as to withstand environmental exposure for about 25 years. Duringthat time, the degradation of conversion efficiency may be less thanabout 10% loss over the course of 12 years in a typical outdoorinstallation, less than about 20% loss over the course of 25 years. Theoptical transparency may be such that in one embodiment, opticaltransparency comprises of less than 5% haze, preferably less than 3%haze, most preferably less than 1% haze. Although not limited to thefollowing, electrical insulating capability may involve a resistivitygreater than 10̂9 ohm*cm, preferably greater than 10̂12 ohm*cm, mostpreferably greater than 10̂15 ohm*cm. The substantially organic barriermaterials, substantially inorganic barrier materials, and/or hybridbarrier materials may be applied via vacuum and/or non-vacuum techniquesas described herein and are not limited to one type of technique or theother.

Although CIGS solar cells are described for the purposes of example,those of skill in the art will recognize that any of the embodiments ofthe present invention can be applied to almost any type of solar cellmaterial and/or architecture. For example, the absorber layer in solarcell 10 may be an absorber layer comprised of organic oligomers orpolymers (for organic solar cells), bi-layers or interpenetrating layersor inorganic and organic materials (for hybrid organic/inorganic solarcells), dye-sensitized titania nanoparticles in a liquid or gel-basedelectrolyte (for Graetzel cells in which an optically transparent filmcomprised of titanium dioxide particles a few nanometers in size iscoated with a monolayer of charge transfer dye to sensitize the film forlight harvesting), copper-indium-gallium-selenium (for CIGS solarcells), CdSe, CdTe, Cu(In,Ga)(S,Se)₂, Cu(In,Ga,Al)(S,Se,Te)₂, and/orcombinations of the above, where the active materials are present in anyof several forms including but not limited to bulk materials,micro-particles, nano-particles, or quantum dots. The CIGS cells may beformed by vacuum or nonvacuum processes. The processes may be one stage,two stage, or multi-stage CIGS processing techniques. Additionally,other possible absorber layers may be based on amorphous silicon (dopedor undoped), a nanostructured layer having an inorganic poroussemiconductor template with pores filled by an organic semiconductormaterial (see e.g., US Patent Application Publication US 2005-0121068A1, which is incorporated herein by reference), a polymer/blend cellarchitecture, organic dyes, and/or C₆₀ molecules, and/or other smallmolecules, micro-crystalline silicon cell architecture, randomly placednanorods and/or tetrapods of inorganic materials dispersed in an organicmatrix, quantum dot-based cells, or combinations of the above. Many ofthese types of cells can be fabricated on flexible substrates.

Embodiments of the present invention may also be applied to solar cellswith the following features. It should be understood that the P-typelayer may be either organic or inorganic. Alternatively, the N-typelayer may be either organic or inorganic. The possible combinations mayresult in an inorganic P-type layer with an inorganic N-type layer, aninorganic P-type layer with an organic N-type layer, an organic P-typelayer with an inorganic N-type layer, or an organic P-type layer withand organic N-type layer. By way of nonlimiting example, suitableinorganic materials for the P-type and/or N-type layer include metaloxides such as titania (TiO₂), zinc oxide (ZnO), copper oxide (CuO orCu₂O or Cu_(x)O_(y)), zirconium oxide, lanthanum oxide, niobium oxide,tin oxide, indium oxide, indium tin oxide (ITO), vanadium oxide,molybdenum oxide, tungsten oxide, strontium oxide, calcium/titaniumoxide and other oxides, sodium titanate, potassium niobate, cadmiumselenide (CdSe), cadmium suflide (CdS), copper sulfide (e.g., Cu₂S),cadmium telluride (CdTe), cadmium-tellurium selenide (CdTeSe),copper-indium selenide (CuInSe₂), cadmium oxide (CdO_(x)) i.e. generallysemiconductive materials, as well as blends or alloys of two or moresuch materials.

Embodiments of the present invention may also be applied to solar cellswith the following features. By way of nonlimiting example, suitableorganic materials for the P-type and/or N-type layer include conjugatedpolymers such as poly(phenylene) and derivatives thereof, poly(phenylenevinylene) and derivatives thereof (e.g.,poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene (MEH-PPV),poly(para-phenylene vinylene), (PPV)), PPV copolymers, poly(thiophene)and derivatives thereof (e.g., poly(3-octylthiophene-2,5,-diyl),regioregular, poly(3-octylthiophene-2,5,-diyl), regiorandom,Poly(3-hexylthiophene-2,5-diyl), regioregular,poly(3-hexylthiophene-2,5-diyl), regiorandom), poly(thienylenevinylene)and derivatives thereof, and poly(isothianaphthene) and derivativesthereof. Other suitable polymers include organometallic polymers,polymers containing perylene units, poly(squaraines) and theirderivatives, and discotic liquid crystals. Other suitable organicmaterials include organic pigments or dyes, azo-dyes having azochromofores (—N═N—) linking aromatic groups, phthalocyanines includingmetal-free phthalocyanine; (HPc), perylenes, perylene derivatives,Copper pthalocyanines (CuPc), Zinc Pthalocyanines (ZnPc),naphthalocyanines, squaraines, merocyanines and their respectivederivatives, poly(silanes), poly(germinates),2,9-Di(pent-3-yl)-anthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10-tetrone,and2,9-Bis-(1-hexyl-hept-1-yl)-anthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10-tetroneand pentacene, pentacene derivatives and/or pentacene precursors, anN-type ladder polymer such as poly(benzimidazobenzophenanthrolineladder) (BBL), or any combination of the above.

For any of the embodiments herein, it should be understood that the anyof the types of protective layers may be used in single or multiplecombination with one another. As a nonlimiting example, Table I showssome possible combination of layer types used in combination over asolar cell. Other embodiments may combine all three types of layers inany order over the solar cell. In the embodiments combining all threetypes of layers, some may have multiple layers of the same material.Some three type and/or two type embodiments may have multiple layers ofthe same material such as alternating layers of organic and inorganiclayers. Some may have two or more layers of one type of material andthen at least one or more layers of a second type of material. In yetanother embodiment, there may be only one type of material but multiplelayers of that one material.

TABLE I Hybrid Organic Inorganic Organic/Inorganic OrganicOrganic/Organic Organic/Inorganic Organic/Hybrid InorganicInorganic/Organic Inorganic/Inorganic Inorganic/Hybrid HybridHybrid/Organic Hybrid/Inorganic Hybrid/Hybrid Organic/Inor- ganic

Additionally, concentrations, amounts, and other numerical data may bepresented herein in a range format. It is to be understood that suchrange format is used merely for convenience and brevity and should beinterpreted flexibly to include not only the numerical values explicitlyrecited as the limits of the range, but also to include all theindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. Forexample, a thickness range of about 1 nm to about 200 nm should beinterpreted to include not only the explicitly recited limits of about 1nm and about 200 nm, but also to include individual sizes such as butnot limited to 2 nm, 3 nm, 4 nm, and sub-ranges such as 10 nm to 50 nm,20 nm to 100 nm, etc. . . . .

The publications discussed or cited herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.All publications mentioned herein are incorporated herein by referenceto disclose and describe the structures and/or methods in connectionwith which the publications are cited.

While the above is a complete description of the preferred embodiment ofthe present invention, it is possible to use various alternatives,modifications and equivalents. Therefore, the scope of the presentinvention should be determined not with reference to the abovedescription but should, instead, be determined with reference to theappended claims, along with their full scope of equivalents. Anyfeature, whether preferred or not, may be combined with any otherfeature, whether preferred or not. In the claims that follow, theindefinite article “A”, or “An” refers to a quantity of one or more ofthe item following the article, except where expressly stated otherwise.The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase “means for.”

1. A flexible solar panel comprising: a plurality of solar cells;wherein the solar cells are covered on at least one surface by amulti-layer film having one or more layers of a first material and oneor more layers of a second material, wherein the multi-layer filmcontains randomly located pinholes or gaps at interfaces between layersthat define long tortuous pathways that slow water penetration throughthe multi-layer film; wherein a plurality of particles each sizedbetween about 1 nm to about 10 microns which are contained in themulti-layer film to block tortuous pathways through the film, wherein atleast a portion of each of the particles is in contact with one of thelayers of the first material or one of the layers of the second materialand wherein substantially all of the tortuous pathways are blocked by-atleast one of the particles.
 2. The flexible solar panel of claim 1wherein the multi-layer film comprises at least one material selectedfrom the group consisting of: silica, alumina, aluminosilicates,diamond-like films, borosilicates, silicon nitride,aluminophosphosilicates, aluminophosphates Niobium oxide (Nb₂O₅),Niobium nitride (NbN), Zirconium Oxide (ZrO₂), Zirconium Nitride (ZrN),Hafnium Oxide (HfO₂), Hafnium nitride (HfN), Zinc oxide (ZnO), Yttriumoxide (Y₂O₃), Cerium Oxide (CeO₂), Scandium Oxide (Sc₂O₃), Erbium oxide(Er₂O₃), Tantalum oxide (Ta₂O₅), Tantalum nitride (TaNx), Vanadium oxide(V₂O₅), Indium Oxide (In₂O₃), Aluminum nitride (AlN), Titanium Nitride(TiN), Molybdenum nitride (MoN), Gallium nitride (GaN), Lanthanum oxide(La₂O₃), Zinc Sulfide (ZnS), Tin oxide (SnO₂), strontium sulfide (SrS),calcium sulfide (CaS), lead sulfide (PbS), indium tin oxide (ITO),tungsten oxide, calcium/titanium oxide, and/or combinations thereof. 3.The flexible solar panel of claim 1 wherein the multi-layer filmcomprises of a nanolaminate comprised of at least one materialcombination selected from the group consisting of: hafniumoxide/tantalum oxide, titanium oxide/tantalum oxide, titania/alumina,zinc sulfide/alumina, ATO, AlTiO, and/or combinations thereof.
 4. Theflexible solar panel of claim 1 wherein the multi-layer film comprisesof a first layer of a first inorganic material and a second layer of asecond inorganic material. hafnium oxide/tantalum oxide, titaniumoxide/tantalum oxide, titania/alumina, zinc sulfide/alumina, ATO, orAlTiO
 5. The flexible solar panel of claim 1 wherein the multi-layerfilm comprises of a layer of silica layer and a layer of alumina.
 6. Theflexible solar panel of claim 1 wherein the multi-layer film comprises aplurality of fused inorganic particles.
 7. The flexible solar panel ofclaim 1 wherein the multi-layer film comprises a plurality of fusedsilica particles.
 8. The flexible solar panel of claim 1 wherein themulti-layer film is a layer deposited by atomic layer deposition.
 9. Theflexible solar panel of claim 1 wherein the multi-layer film comprisesof a plurality of layers deposited by atomic layer deposition.
 10. Theflexible solar panel of claim 1 wherein the multi-layer film comprisesof a silico-acrylic composition.
 11. The flexible solar panel of claim 1wherein the multi-layer film comprises: a plurality of layers of aninorganic material; and a plurality of layers of an organic materialwherein the layers of organic material alternate with the layers ofinorganic material; wherein adjacent layers of the organic material andthe inorganic material are covalently bonded layers characterized bycovalent bonds that couple adjacent layers together.
 12. The flexiblesolar panel of claim 11 wherein each of the layers of inorganic materialhas a thickness of about 0.1 nm to about 1 nm; about 1 to about 10 nm;or about 1 nm to about 100 nm.
 13. The flexible solar panel of claim 1wherein the multi-layer film has a water vapor transmission rate (WVTR)sufficiently low so that there is substantially no loss in solar cellconversion efficiency when the cell is exposed for 1000 hours at 85° C.and 85% relative humidity.
 14. The flexible solar panel of claim 1wherein the multi-layer film has a WVTR such that the conversionefficiency of a cell with the multi-layer film has a conversionefficiency at least 25% better than an unprotected cell after both areexposed for 1000 hours at 85° C. and 85% relative humidity.
 15. Theflexible solar panel of claim 1 wherein the multi-layer film layer has aWVTR such that the conversion efficiency of a cell with the multi-layerfilm has a conversion efficiency at least 50% better than an unprotectedcell after both are exposed for 1000 hours at 85° C. and 85% relativehumidity.
 16. The flexible solar panel of claim 1 further comprising ananti-reflective layer above the multi-layer film.
 17. The flexible solarpanel of claim 1 wherein the multi-layer film has anti-reflectivequalities.
 18. The flexible solar panel of claim 1 wherein the particlesare comprised of a material selected from the group consisting of:silica, glass, or other transparent inorganic materials.
 19. Theflexible solar panel of claim 1 wherein the particles have a shapeselected from the group consisting of: spherical, platelet, or flake.20. The flexible solar panel of claim 1 wherein the particles are sizedto be within 5-10% of each other.